ECU: Connect 1993-1993 Turbo ECU to 1991-1999 NA Harness
Here is a little guide for people who have questions about connecting a 1G TT ECU to their 2G NA Harnesses. This is information that I have either collected through research or through my own personal experience. Much kudos go out to John aka J-GROOVE for his part in this info. Here we go:
Front O2 pin 55
Rear O2 pin 56
1st gen TT FED SPEC ECU with my '95 N/A harness.
At the O2 sensor:
At the O2 connector:
At the ECU:
Those should be the colors that you should be looking for. You know how the old O2 sensor came from under the car? Well extend all of those wires up to the engine bay and that O2 sensor will be ur rear one. Once u have done that, make it so that the stock heater and ground wires also go to connect to the front O2 sensor's heater and ground wires. Then Cut the O2 signal wire from the rear O2 sensor so that it no longer travels under the car. Then lengthen that signal wire and run it through the firewall to the ECU and wire it into pin number 56 (Rear). Then take the signal wire from the front and lengthen it, run it through to firewall to pin 55 for the front. Now, if I recall correctly pin 55 is empty, I will tell you what to do about that in a second. To correctly install a TT ECU and have it not blow itself up in an NA car, you will need to cut a few wires. Cut the wire to pins 103, 109, 110 and 111. Those are for stuff that our cars won't even use. Here's a pic to aid in the explanation:
Now for hooking up the signal wires.... If there is a wire in the pins u can just splice in your new connection. If not, you will have to take a pin connector and the wire from one of the pins that are no longer in use (103, 109 etc) and swap it into pin 55 and/or pin 56 so that u can splice in ur signal wire. So make sure that when you cut those that you leave quite a bit of wire to work with. There are two different types of harnesses that I know of. One of them opens up real easy and one you can't open and can only slide the pin connector out. For the one that can't open, You need to press down on the metal clip thingy to get it out. I used a needle.