Mazda MX-6 Forum banner
1 - 20 of 73 Posts

418 Posts
Discussion Starter · #1 · (Edited)

This how-to will cover Megasquirting your 1st gen Probe/MX6 Turbo!

This is a Plug-n-Play how-to. This means YOU can Megasquirt you car will basic hand tools and a little time. I reveal all the steps and secrets to get YOUR car RUNNING!!!

This also allows you to return to stock and any time without alot of work. With this assembly, we utilize the factory wiring harness and factory distributor (modified) and coil.

This how-to covers the most common type of Megasquirt. MS1 V3.0. This offers excellant benifits at a affordable price. This version offers a wide range of upgrades and support.

PLEASE NOTE!!!! This covers STOCK engine running STOCK injectors running a STOCK turbo on 6-7 psi of boost. YOU WILL have to tune outside this setup, and may have to tweek the tuning listed here, as no two engines are them same. I am not out to tune your engine, but I will get you started and a baseline to start from.

PLEASE NOTE!!! This is currently for 88-89 ONLY! 90-92 IS ON THE WAY!!!

Current Statis-In Final Tuning. has been tested and works, just have to get my ve tables and after-start enrichment finished.

418 Posts
Discussion Starter · #2 ·
Step 1: Ordering whats needed (MS components and tools)


Only basic hand tools are required for assembly.

* Soldering Iron- I used a 30-watt basic iron to build mine, you need nothing more. You are going to solder small components, it will provide plenty of heat. I picked up mine at a local Radio Shack in a kit for $7.99

Soldering Iron-Radio Shack

* De-soldering Tool- Accidents happen, be it simply touching an empty "pad" on the board with a tip covered with solder, or soldering a component in the wrong spot or wrong orientation. Its a cheap tool that is a definate life saver. Avalible at Radio Shack for $9.89..

Desoldering Tool-Radio Shack

* Solder- I used .022" diameter, rosin-core solder. Also I used Silver Bearing, although not required when building the MS. This is a thin-wire solder, which is helpful since you will be working on small compnents in tight places. $5.89 at Radio Shack.

Solder-Radio Shack

* Heat-Sink Compound- If you buy a kit it will have some, but not really enough...Go ahead and buy a small tube. $2.99 at Radio Shack.

Compound- Radio Shack

* Electrical Multimeter- This is used to test a few things on the MS when assembling, and helps troubleshoot and insure that you have good joints.

* Phillips head and thin flat blade screwdriver- Used for various screws.

* Small diagonal cut pliers- For cutting off the ends of component leads after soldering.

* RTV Silicone-You only need a drop, its used to "cushion" one of the on-board compnents.

MS and Componets-

I HIGHLY RECOMMEND dealing with Megasquirt Kits / Assembled Engine Management Systems, Wideband o2 Sensor Systems and tuning products . They offer a full selection of MS related comoponents, awesome customer service, and super fast shipping. They are also the cheapest way to go that I have found (for new components).

* Megasquirt- You want to order Megasquirt 1 v.3.0. This is what this write-up pertains to. It is the all-around easist way to go.

You can either order a assembled unit and save about 8 hours of work, or build it yourself following the how-to. If you get a assembled unit, be sure to tell them you will be running a missing tooth wheel with a single coil.

If you decide to do it yourself, I suggest you buy the megasquirt in a kit form, this insures you have everything you need and that all components will match. When you purhase from diy auto tune, you will have virtually everything you need to build the basic MS. Another great thing about dealing with them, is that each component comes pre-labeled, individually bagged, and seperated according to component type. You also get a well built case. I purchased mine for $187.00.

Megasquirt I-V3.0-Kit

* MegaStim - This is A MUST in order to reliably test your megasquirt. Its a little bit extra to add to the bill, but if you are wanting to assemble your own, you need this to make sure you are assembling a working unit. I have used the standard V2.2, but they now offer a newer "JimStim", which allows you to test differant ignition setups by simply changing wire "jumper" postions. If you are building a standard MS for a single coil, distributor car (such as the probe), then a standard one is all you need. If not, Id go with the JimStim. Kits for the Standard v2.2 is $45.00, the JimStim $56.00.

This is also a great "starter" for those that are beginning to solder. Lets you get the hang of it without risking messing up the real MS. It is also a great tool for learning about how megasquirt works and tuning.

BTW, BUY THE A/C POWER ADAPTER!!! Its only a few bucks more, but it saves time and money on using 9v batterys. They DO NOT LAST!! They only last a few minutes, and sometimes will cause you to think there is a problem with your MS when acually you just have a bad battery. Its only $7.50 Power Adapter

Standard V2.2 MegaStim

JimStim Stimulator

Megastim (assembled)-

JimStim (assembled)-

IC Sockets These are the only things that are not in the kit that should be. Since IC chips are EXTREMELY sensitive to heat, this insures you wont burn one up by soldering. They aren't required, but for less than $5.00, its cheap insurance.

you'll need one 16 pin, two 8 pin, and a 6 pin. Radio shack sells them all except the 6 pin, but you can easily modify a 8 pin to work, and thats what I did and will show you how in the assembly section.

List of IC Sockets

* Tuning Cable- Just a simple DB9 cable, BUT make sure that it is a true straight-thru cable...meaning that pin 1 on one end is connected to pin 1 on the other, etc... (tested useing a ohmmeter). They are $5.50 from, so I would just get one when you order your MS to insure you get te right one.

DB9 Cable

* Laptop/Desktop- For construction and testing, you can use your desktop, just as long as you have the correct DB9 connector on the back and the apropriate software (located in the assembly section). You will, however, need a laptop for tuning in car. You DO NOT need a new one, in fact, the older ones are best, as they have the DB9 connector where as most newer one do not.

Step 2: Assembly and Testing

DO NOT let this be your first time soldering....Do a internet search on soldering before attempting assembly of megasquirt...Please make sure you are comfortable and confident enough before tackling this project, or you will be wasteing your time and money...

You can either:

A)Buy a "starter" kit and practice, usally these are simple projects (such as a blinking LED) but offer great practice in circuit building, and allows you to successfully learn to solder....

B)Go to Radio Shack and buy a simple blank circuit board ($3) and a pack of resistors ($4) and practice soldering the joints to the board.

All assembly steps are covered in megamanual in the links posted below. I am not going to do a step by step assembly, as that would be a pointless waste of my time and forum space. It is detailed precisly in the links below, and layed out in a easily read format.

V3.0 Assembly (MSI and MSII)

MegaStim Assembly V2.2

However, I will touch on some basic points and give pictures for referance.

Agian, the following pics are for Megasquirt I - V3.0 so the board/components may differ slightly depending on what you decide to order.

Be sure to assemble your MegaStim before starting on the megasquirt itself, as its needed at the end of each section for testing!!!!

418 Posts
Discussion Starter · #3 · (Edited)
Power Supply:

Complete steps 1-23, soldering the components to the board.

***Be sure to observe the correct orentation of all diodes and capacitors. Unless you are blind or stupid, there really isn't a way to screw up as long as you pay attention. The proper direction is cleary explained in each step that involves requires soldering one to the board, and the silkscreen on the board shows the "+" for capacitors, and "stripe" for diodes.***

Board with connectors installed and CPU socket installed (steps 1-3):

Proper mounting of Voltage Regulator. (U5, step 21) This is also how all components mounted to the heat sink should look. DON'T FORGET THE HEATSINK COMPOUND! Be easy when bending the leads, dont over stress them, they could break (think of a bending paper clips). Use a nylon screw for mounting this one, and trim the excess of the screw off the bottom after mounting.:

This is the board after the power circuit is completed. Also notice I have already installed all of my IC sockets, now is a good time to go ahead and solder them in:

*After completion, hook up your MegaStim, and test that you have power across the specified pins at the CPU socket. (see assembly guide for pin locations). the chart is below step 23.

*Its also a good idea to check that you have 8-9 volts at your voltage regulator (U5) on the pin closest to the DB9 connector, a good, solid ground at the center pin-to-heatsink (less than 1 ohm resistance), and 5 volts at the pin closest to the DB39 connector.

If everything passes the test, your good to go ahead to the next section.

If not, STOP, go back and check everything before proceeding! Make sure that all components are installed (its easy to miss one sometimes), make sure capacitors and diodes are in the right orientations, you have good solid soldered joints, and if you opted to use a 9v battery to power the MegaStim, be sure you have a fresh, new battery (most common problem).

Serial Communications Construction & Testing

Complete steps 24 and 25.

***Be sure to observe the correct orientation of all diodes and capacitors. Unless you are blind or stupid, there really isn't a way to screw up as long as you pay attention. The proper direction is clearly explained in each step that involves requires soldering one to the board, and the silkscreen on the board shows the "+" for capacitors, and "stripe" for diodes.***

With this, you have enough to test your megasquirt's communications.

You MUST verify that you have a true “pass-thru” db-9 cable. This means that pin 1 goes to pin 1 on the opposite connector, pin 2 goes to pins 2 on the opposite connector, etc. You can test this easily with an ohmmeter.

To test the communications part of the megasquirt, you need HyperTerminal. If you are using an older computer/laptop to tune and test your megasquirt, then most likely it is already on the computer.

To check, go to start menu -> programs -> accessory’s -> communications. You should find it under this.

If you don’t have it, you can download it for free by clicking on the link provided in the assembly section of Megamanual.

Once you have HyperTerm, Take your db-9 cable and using alligator clips or a small piece of wire, connect pins 2 & 3. By jumpering these two, we are providing (in shortest terms) a "u-turn" for information coming out of the computer. This step ensures that we have HyperTerm properly setup on our computer so that we accurately and reliably test communications on megasquirt. All information sent through the output pin will be "u-turned" back into the input pin.

Plug the cable into your computer/laptop, but not your megasquirt. IMPORTANT! Do not let the alligator clips or wire touch the metal casing around the plug or you will not get the proper results!

Start HyperTerm by clicking on the icon. Start a new connection by typing in a name, such as megasquirt. Click OK.

Next, a “connect to” box will appear. Under “connect using”, select your COM port. Most will use COM1, so try this first. Select OK.

You will then have a “port settings” box pop up. Set all parameters to those shown below. (Megasquirt 1)

With that done, you should be able to hit any key on the keypad and have that digit show up in the dialog box. If not, double check all settings, COM port, and proper pins selection on the cable.

Now that we have HyperTerm tested, we can now test the communication on the megasquirt. Remove the ”jumper” from the end of the cable and plug it into the MS.

We no want to Jumper pins 12 & 13 on the 40-pin processor socket. This is going off teh same concept described earlier when we "looped" the DB-9 cable. This is providing a "u-turn" for information so we can determine that our megasquirt will respond to our laptops when we tune.

The pins are right beside the “R44” resistor/location.

Plug in you stimulator (told ya you needed one) and power it up. You should now be able to type any letter/number into HyperTerm and it should show up on the screen.

Clock Circuit assembly and testing
Complete steps 27-37.

***Be sure to observe the correct orientation of all diodes and capacitors. Unless you are blind or stupid, there really isn't a way to screw up as long as you pay attention. The proper direction is clearly explained in each step that involves requires soldering one to the board, and the silkscreen on the board shows the "+" for capacitors, and "stripe" for diodes.***

Complete step 38. NOTE: Use CAUTION when handling the crystal. It is VERY fragile and can be destroyed easily. Once soldered in place, bend down slightly into a small dab of RTV silicone. This will help dampen shock and vibrations, insuring trouble-free operation.

Complete step 39. NOTE: Use CAUTION when installing the processor. The “legs” are thin and fragile. Be sure ALL “legs” are in the socket before firmly pressing it down into place or damage can occur. Some straightening of the legs will be necessary and is normal. They bend very easily, just be sure to use care when doing so…don’t over bend or they can break!

We are now ready to test.

You must download and install Megatune at this time in order to test the clock circuit. You can find the link under the clock circuit assembly section in Megamanual.

Once you install Megatune, click on the icon to start testing. For now, when “Select Project” box appears, click “MS1 Original BG Code”.

When MegaTune appears, click “File”, and “Configuator”.

Click the “plus sign” to pull down the menu. Select “code_variant”.

Ensure in the upper box that “MS_1 – Bowling and Grippo Megasquirt”

Once all this is complete, go to “file” and select “run Megatune”.

Plug in the DB-9 cable from your PC/Laptop to your Megasquirt, and then connect your stimulator. With Megatune, Under “tuning” select “real-time display”.

You should see the time counting up every second. If this is up and running, you are good to move to the next step.

If not, STOP, go back and check cable connections and that you have a good battery (if running 9v on the stimulator, the most common problem). These last only a few minutes during testing. If all that looks, good, go back and check all solder joints and connections (and hope you handled the “crystal” carefully like I told you earlier!)

418 Posts
Discussion Starter · #4 · (Edited)
Input Section Construction & Testing

***Before Starting this section of assembly, REMOVE the processor from the 40-pin socket - use a thin screwdriver and pry it from the socket, first one end, then the other - place it back on the foam pad it was shipped with.***

***Be sure to observe the correct orientation of all diodes and capacitors. Unless you are blind or stupid, there really isn't a way to screw up as long as you pay attention. The proper direction is clearly explained in each step that involves requires soldering one to the board, and the silkscreen on the board shows the "+" for capacitors, and "stripe" for diodes.***

Complete steps 43-49.

Now comes a decision. Megasquirt allows you to choose how you want to setup your "tach" (rpm) signal to megasquirt, via either a “Hall” sensor, or “VR” sensor. The one you want is “VR” sensor, as this is what the factory turbo distributor uses. However, Megasquirt does recommend installing both circuits and selecting either/or by “jumpers”, but you don’t necessarily need to install both.

If you want to install both circuits, complete steps 50 ( “a” only) & 51.

If you only want what you need, complete step 51 ONLY.

I installed only the “VR” circuit (step 51), as this is the only input i'll personally ever use. If you THINK the possiblility of ever having to sell your megasquirt, you may want to go ahead and install the Hall sensor circuit as the future potential buyer may need that type of input. You arent loosing or gaining anything by installing it, as you already have the components in the kit...will only cost you a few minutes of soldering.

Here are some things to pay attention to under step 51 for installing the VR sensor input circuit.

“g”à Install the “trimmer potentiometers” with the adjustment screw pointing towards the heatsink. Turn the screw on “R52” and "R56" all the way counter-clockwise until you hear a "click"

“k” à Use CAUTION when soldering these, as the “leads” are very thin and you can accidentally “bridge” these by using too much solder. Clean your tip before installing, and use the solder sparingly.

Complete Step 52 by installing the following jumpers for the “VR” circuit.

*Jumper VRIN to TACHSELECT on the bottom side of the PCB (near the DB37, opposite the heat sink.)

*Jumper TSEL to VROUT on the bottom side of the PCB, near the center.

Complete step 53 by installing the map sensor. This mounts from the bottom of the board.

Finish assembly of this section by completing step 54, then we move on to testing.

Re-install your processor (40-pin), DB-9 cable, and stimulator. Open Megatune and select Real-time display (same as from “Clock Circuit” testing).

You can now turn the adjustment knobs on your stimulator. You should see the values on the screen change as you turn the knobs.

Follow step 55 for testing each value (RPM, EGO, Map, etc.).

If everything tests fine and all values respond, unplug the stimulator and DB-9 cable and move on to the next steps.

If not, STOP, go back and assure all components are installed and properly orientated.

Output Section Construction & Testing

***Be sure to observe the correct orientation of all diodes and capacitors. Unless you are blind or stupid, there really isn't a way to screw up as long as you pay attention. The proper direction is clearly explained in each step that involves requires soldering one to the board, and the silkscreen on the board shows the "+" for capacitors, and "stripe" for diodes.***

Complete steps 56-64.

Step 65-
The only thing to solder on from the component list is “Q16”. DO NOT install R43 OR R57. R43 and R57 are NOT needed when running a single coil from the megasquirt. For more details on this, refer to the MSnS hardware manual by clicking the link below.

MSnS Extra Ignition Hardware Manual

Be sure that you are using the mica-insulators and heat-sink grease when installing Q16.

Install a “jumper” where “R43” would normally sit. Use some decent gauge wire (nothing very thin).

Install a “jumper” between IGBTOUT and IGN. This is located on the bottom of the board between where R43 would sit and the DB39 connector. You can use a snipped lead from a resistor or other electrical component.

We now want to install a “jumper” between IGBTIN and the top of “R26”, but with a 330Ohm resistor between them. You can find a resistor at your local radio shack for a few cents. You want a 330-Ohm, ¼ watt resistor.

First, solder one end of the 330 Ohm resistor to the top leg of “R26”, which is located right beside the “proto area” on the board, and beside the “D14” LED light. You can locate the resistor in the “proto area”

Next, place the other leg of the resistor through a hole in the proto area. On the bottom of the board, solder one end of a piece of wire to the end of the 330Ohm resistor. If you purchased a “kit”, then you should have a piece of jumper wire just the right length. If not, find a small piece.

Solder the other end of the wire to IGBTIN. This is located right beside where we just soldered a jumper for “IGBTOUT & IGN”.

Complete steps 66-68.

Complete step 69 & 70. Megasquirt recommends installing BOTH PWR circuits.

NOTE: When installing “Q9” and “Q12” under step 69, make sure that the metal tab of each does not touch the heatsink. Use the special plastic protectors and washers when installing these. You can use an ohmmeter to verify that there is proper resistance between the two.

Complete step 71.

Note” Megasquirt states to mount these on the heatsink, but from my experience it’s nearly impossible to bend the leads in order to do this. They break VERY easily when you try to bend them. I installed mine “straight up” with no issues. The choice is yours…

Complete steps 72-80 (skip 78-79 if you bought a kit that includes the case).

Install the LED’s and bend them to match the holes on the case end.


You can now fully test your megasquirt by following the paragraph after step 80. If all tests ok, we can move on! If not, STOP, go back and assure all connections are good, all components are in and positioned in the correct orientation.

Before continuing to wiring and tuning, we must first install the MSnS code so we can control both fuel and spark. To do this, we must visit the MSnS website at:

Scroll down the page and find the link that says “ How to load the MS-1 Extra code to the MS ECU”.

The page is very detailed on how to download the code, so I won’t go into detail. Just be sure to read the directions and follow them. The “boot loader" is located right beside the main 40-pin chip and right above the “proto area”

Once you have successfully loaded the new code, continue to “Wiring Megasquirt”.

418 Posts
Discussion Starter · #5 · (Edited)
Wiring Megasquirt into your 1st gen Probe/MX6 Turbo

I have decided that the average person is not going to want to make an entire new engine wiring harness, as this is unnecessary for the average user. We can accomplish what we want with the factory harness. With this said, I will show how to make a “plug-n-play” harness. Not only does this make installation easier, but also allows you to return the car to “stock” fairly easily if the need arises.

To wire megasquirt into your car, you will need the following items:

-Turbo Distributor (if you don’t want to destroy your original)
-ECU (same as above)
-GM coolant temp sensor, with connector (either new or junkyard)
-GM OPEN element IAT sensor, with connector (either new or used)
-N/A thermostat housing (one with 2 sensor bungs)
-Wideband O2 Sensor and controller (for tuning)
-Various wire connectors
-Electrical tape

Modifying the turbo distributor.

NOTE: This is currently for the 88-89 ONLY!! 90-92 WILL be posted soon!!!!

For Megasquirt, we need a RPM input. The simplist way to achive this input on the turbo engine, is using the factory VR sensor and trigger wheel. BUT, in order to do this, we must modify the factory 24-tooth wheel so the VR sensor can provide the signal in terms that Megasquirt can reconize. Since RPM is based on the rotations of the crankshaft, and the pick-up wheel is located in the distributor where the camshaft turns at half the speed of the crank, we must set up the distributor in a way to "trick" the MS in to thinking we are triggering off the crank. We can achive this by removing two teeth from the factory pick-up wheel in the distributor. This spits the wheel in half, giving us a 12-1 wheel (11 teeth, one missing). This allows us to split the cam cycle into two seperate cycles to match the crankshaft. The first tooth starts the ignition pick-up cycle, and the missing tooth signals for the megasquirt to "start over" the ignition event.

To start the modifications, remove the cap, rotor, and protective cap.

Remove the two sensors on top by first removing the 4 phillips screws (2 per sensor). Then cut the wires attached to the sensor and discard them.

You should now have this:

Next, remove the “spacer plate” retaining screws. Lift out the plate and discard.

Next, remove pin from drive “gear” on the cam side of the distributor. You can use a hammer and punch. Using a sharpie or equivalent, make a spot on the “gear” and the shaft, this way you can re0assemble them back together correctly.

Inside the distributor, remove the two phillips screws at the bottom. This holds in the center shaft. Once removed, you should be able to easily remove the distributor shaft.

We can now modify the distributor to work with megasquirt. We want to modify the bottom wheel, not the top. You want to grind down two of the “teeth”. Looking at the top wheel, at the point, count back four teeth. We want to remove the forth tooth. Mark this tooth.

We also want to remove the tooth directly opposite of this one. Count 12 teeth (in either direction). Make the 12th tooth. Make this tooth, as we want to remove this one as well. You should have 11 teeth between the two marked teeth on both directions.

Now, grind down the two teeth. You can use a Dremal tool, a drill with a grinding/cutting bit, air tool, etc. TAKE YOUR TIME! Go slow and take off a little at a time. We are working in a small space with very little material, and you DO NOT want to damage the surrounding teeth. If you happen to “nudge” one, its no big deal, just try to avoid them as much as possible.

This is what you want:

Once this is complete, clean the distributor shaft of ALL metal shavings. Re-assemble the distributor shaft into the distributor housing. Install mounting screws. Reinstall the distributor drive gear and retaining pin. Be sure to line up the marks you made earlier.

Re-install the rotor and cap and your done!

Getting “pig-tail” connector from ECU[/B

NOTE: Shown in pics is a 1989 N/A ECU. Turbo ECU's will be simalar, only more stuff will have to be removed. Your goal is to get the factory connector.

Remove the top plate retaining screws.

Remove the ECU mount retaining screws (all four corners).

Remove the bottom plate retaining screws.

Go around the outside of the ECU and remove any remaining screws.

On the bottom of the ECU, remove the four screws retaining the circuit board.

Remove the board from the ECU case. Discard the case and all remnants.

Remove the two screws holding the connector to the board. These may be covered in solder, so use a pair of pliers to remove.

Remove all surrounding electrical components near the connector. This will give you access to cut the connector legs and remove the clip.



Using some wire snips (smaller the better), start clipping the connector legs from the board. Start with the long ones first. As you cut, GENTLY bend them upwards so we can access the shorter ones.

After all the legs have been cut, GENTLY bend all the legs straight. Then, trim the longer legs to approximately the same length as the shorter ones.

You now have your connector ready to make a pigtail. Before we proceed, we want to mark the clip to aid us in making the pigtail.

Hold the connector with the “legs” pointing towards you, and with the “holes” facing up. Using a fine point sharpie, number the columns of legs from 1-26, starting from the left.

Next, mark the top of the connector (side with holes) “A”.

Mark the bottom “B”.

This will allow you to follow the wiring chart with ease. Examples: “2A” would be the “leg” in column 2, upper row of “legs”. “19B” would be in column 19, bottom row of “legs”.

418 Posts
Discussion Starter · #6 · (Edited)
Making a “Plug-n-Play” Harness

NOTE: This is currently for the 88-89 model ONLY! 90-92 will come soon!

We can now start making our “pigtail”.

Start by warming up your soldering iron. While this is warming, you can begin cutting some sections of wire. The length of the strips depends on where you want to mount you ECU. A minimum would be roughly 1 foot. You will need roughly 15 strips. Be sure to cut them al to the same length.

Once your soldering iron is warm, we can now begin.

Start by familiarizing yourself with the chart I made below and make sure you understand the system. A number followed by a letter (ex. 7B) is referencing the “factory” connector. When a number is referenced by a “pin’ (ex. “pin 4) it refers to the DB-37 connector that plugs into the ECU.

Here are the wiring locations. This is looking at the BACK if the DB-37 connector, the side where you solder on the wires.

NOTE: This is for 88-89 ONLY!! 90-92 is coming soon!!

Megasquirt Inputs/Outputs-

Pin 2 --> 9A-VR Sensor (+)
Pins 8 & 9 --> 25A-Ground
Pins 10, 11 & 18 --> 22A-Ground
Pin 19 --> 21B & 14A-TPS Sensor Ground
Pin 20 --> 7B-IAT Sensor
Pin 21 --> 8A-CLT Sensor
Pin 22 --> 16A-TPS Signal
Pin 24 --> 10B-VR Sensor (-)
Pin 26 --> 13A-TPS 5 volt
Pin 28 --> 26A-12V Power (ON/START)
Pins 32 & 33 --> 23A-Injectors A
Pins 34 & 35 --> 24A-Injectors B
Pin 36 --> 12B-Ignition Output (Coil)
Pin 37 --> 20A-Fuel Pump Relay

If you need to referance the factory wiring inputs/outputs, see the links below from It includes factory wiring colors and locations on the factory harness connectors.

1989 2.2L 4-Cylinder Turbo Engine

1990-92 2.2L 4-Cylinder Turbo Engine w/Automatic Transaxle

1990-92 2.2L 4-Cylinder Turbo Engine w/Manual Transaxle

The DB-37 connector has numbers stamped onto the face to show the pin locations in case you ever get confused or lost. If unsure, just simply look at the numbers on the connector.

I will show you the first, the rest will be the same. Just follow the chart. Some will show splices, and I will show pics of these.

First, strip one end of a piece of wire. Solder this end onto “9A” (Factory connector). Its best to heat up the connector leg first and apply some solder. DO NOT APPLY TOO MUCH HEAT OR YOU WILL MELT THE FACTORY CONNECTOR! Then, heat up the wire and apply some solder to it. Next, place the wire onto the leg and apply heat to “fuse” the two.

Slide a small piece of heatshrink over the soldered “leg”.

Strip the other end of the wire. Insert into “pin 2” of the DB-37 connector. Apply solder.

That’s it. Just repeat until all are done.

As stated before, some require splicing. Ex. “14A” needs to be spliced to “21B”. The other end of “21B” goes to “pin 19”. Put the wires togeather and apply solder.

Once all connections are made, test them with an Ohmmeter to ensure that all connections are good. GENTLY wrap the wires in electrical tape and install the DB-37 “hood”.

Underhood Wiring

We now have a few connections underhood that need attention.

CLT & IAT Sensors-

We need to install the coolant temp sensor and IAT sensor, and wire them into the harness.

Since we are going for a “return to stock” aspect, we can tap into the extra distributor wires from the two sensors that we removed. This way, we don’t disturb the factory harness, nor do we have to run additional wiring. The distributor is already “destroyed”, so why not modify it some more?

Plug the distributor into the wiring harness. Look at the connector on the wiring harness. Find the “green” wire. Note which wire at the distributor is connected to this. At the base of the distributor, snip the wire and separate from the rest. This will be our IAT Sensor wire.

Now, go back to the factory harness plug and find the “red” wire. Follow the same instructions as above. This will be our CLT Sensor wire.

After the signal wires are connected, combine the grounds.Useing a wiring connector, ground both sensors to the engine.

The IAT Sensor needs to be mounted as close to the throttle body as possible. Simply extend your wiring to reach it.

The CLT Sensor needs to be mounted in the thermostat housing. The easist way to do this is get a thermostat housing from a N/A engine since they have two "bungs" in it. We cant get rid of the one already on our engine as it controls the cooling fans. You can use the extra hole for our sensor. (note: pic shows the factory housing)


Disconnect the factory ignitor. We will be controling spark with the megasquirt. At the ignitor, we need to make a jumper wire and jumper the yellow/red stripe wire at the ignitor plug and tie the other end to the Yellow wire at the coil (or for those who are/want to run a MSD style coil, connect it to the negitive side of the coil). The pic shows the pin at the ignitor plug that needs to be jumpered.


Premium Member
18,203 Posts
As an option, I would use an ignitor from the BP. It's a three wire, instead of the four like ours, and it also mounts in the factory location :)

4,171 Posts
This is the best writeup ever wrote on this forums, You sir deserve a kudos.:tup:

171 Posts
This is the best writeup ever wrote on this forums, You sir deserve a kudos.:tup:
How about a Nobel Prize. Awesome write-up! Wish I had it last summer.

Premium Member
5,011 Posts
you can use the stock CLT sensor and calibrate it to rx7 settings in easytherm. no need to install an extra one

1,080 Posts
if i saw you in person i would shake your hand. this helps out all of us that arent to MS just yet...

Zach you should gold plate this..

Premium Member
18,203 Posts
I will make this a sticky/faq as soon as he's done.

hopefully the tuning section will be more than just road tuning? Maybe some dyno spark tuning? I know that's expensive though. I plan on post my spark map as soon as I'm done dyno tuning. May be in late feb/early march when I do mine.

418 Posts
Discussion Starter · #14 ·
For now its road tuning....My goal isnt to show everyone how to tune it, as everyones setup is and will be differant. My goal is to get someone from kit to idleing/running....everyone must remember that this is on a stock engine and injectors and is meant to be a baseline.

I plan on adding differant options over time, mainly right now my focus is to finish the tune (hopefully this weekend) and then post up the specific info for 90-92. After that, ill show how to use the factory ignitor and coolant sensors IF thats what someone wants...this will never be "done" im sure, as theres endless possibiltys....

But as far as the baseline how-to, I should be done here shortly...just started back work today from holiday vaction, so time will be tight agian....just gotta get back in routine :)

Premium Member
18,203 Posts
just a question, why not use the three wire BP ignitor? easier install process :)

14 Posts
nice job dude. i just installed ms2 while you were doing all this.

i used the ms wiring harness though. made the engine bay clean as heel without all that work. leaves no unused wiring in the bay.

how is your rpm signal, mine sucks if i use a drill i can get 250 - 2500 really stable and accurate. but cranking i cant get a good stable rpm for shit.

Premium Member
18,203 Posts
nice job dude. i just installed ms2 while you were doing all this.

i used the ms wiring harness though. made the engine bay clean as heel without all that work. leaves no unused wiring in the bay.

how is your rpm signal, mine sucks if i use a drill i can get 250 - 2500 really stable and accurate. but cranking i cant get a good stable rpm for [shizzle].
I don't believe the tach wire in the MS harness is shielded like the stocker. I would look for the gray jacketed/insulated wire and use that for your tach signal. I would also tap into that line to run to your tacho in your cluster, as you may lose your tacho after the install :)
1 - 20 of 73 Posts