For people in the UK and possibly Europe!
I had a KLK7 ECU pulled from an 1998 Australian Eunos 800 2.5L (Xedos 9 / Millenia)... as far as I knew it wasn't paired with an immobiliser, but when I compared the internals to the KLH7 in my 1996 UK MX6 it had an identical circuit board. A few minor differences in resistors but 99% the same. I figured the differences were because of the MAF setup on the KLK7 and a VAF setup on the KLH7.
Here comes the kicker... I wired up the MAF and IAT sensors and then plugged the the KLK7 ECU in! .. got a few codes from the diagnostic port which I think they were 11, 23 and 24. Tried cranking the engine but it would not start. Later found out that there was an immobiliser for my KLH7 (the original ECU). Which meant it was highly likely that the KLK7 ECU also had an immobiliser including valid keys, which I did not have, only the ECU.
What I discovered is the 1995+ OBDII versions of the Mazdas came with a Temic Immobiliser box that uses a coil antenna in the ignition lock to read a chip in the key. Once it finds a valid programmed key it then sends a code word to the ECU to enable fuel and spark.
Unfortunately when I put the original ECU back the car would not start, then I found a document on the Temic immobiliser that said if you put in a new ECU or one from another car, or one that has not paired with an immobiliser, that ECU will try to pair itself with the existing immobiliser and if successful will lock itself to this ECU and not allow the original ECU to start the car. OH NO!! REALLY!!
PDF see immobiliser.pdf
see page 3
Is this the reason I can't start the car or have I fried the ECU??
I have now sent the ECU and immobiliser to a specialist (see link) to see what my options are for re-establishing communications. ECU Decode
Will keep you updated on the outcome. If anyone wanted to put a functioning ECU from another car (in UK or Europe) Darren from ECU Decode said, he does this as a service because replacement parts are no longer available, and the car is useless without a functioning ECU.
I hope this helps someone!