Once you return all the interior things back to the way they were, you need to reattach the speedo cable to the transmission. if you did it by just unscrewing the cable from the receptor, just screw it back in. If you took out the speedo gear, make sure everything is clean, and nothing is dirty before putting it back in the tranny, and securing the holding bolt for it.
Now, start your car once everything is back the way it was, and make sure you have idle, temp, speed, and gas all working like they did

and, hopefully you didnt break your tach like i did
Now that you are all done installing your new guages, go show 'em off to your friends and family as soon as it turns dark enough to see them, you'll get a million and 1 good comments on them
-meaty