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Discussion Starter · #1 · (Edited)
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:
Blue - Signal
white - ground
black - heater
black - heater

At the O2 connector
White - signal
black - ground
red - heater
black - heater

At the ECU
black - signal
green w/blue - ground
green - heater
black w/blue - heater

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. **WHEN EXTENDING O2 WIRES, DO NOT SOLDER TWO WIRES TOGETHER! THE SIGNAL WILL NOT READ CORRECTLY! INSTEAD USE CONNECTORS** 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. I hope this helps......maybe it will get stickied. Peace,
-Mr.3000
 

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Discussion Starter · #2 ·
Re: A Guide for connecting a 1G TT ECU to a 2G NA harness

I made this because I have been getting alot of q's lately on how exactly to do this and also because I know that when I was doing this, I was having a hard time. If it wasn't for John, I would prob still be trying to figure it out. Lol!!
 

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Re: A Guide for connecting a 1G TT ECU to a 2G NA harness

nice, good job!
 

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Re: A Guide for connecting a 1G TT ECU to a 2G NA harness

sorry i've been off the boards for a long time so this might be a stupid question. i have a 1995 SL with a TT conversion on it. so i can put a 1st gen TT ECU into my 95 SL "plug and play" with these pin/wire mods and get the benefit of a TT's fuel MAP?

Jon
 

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Discussion Starter · #7 ·
Re: A Guide for connecting a 1G TT ECU to a 2G NA harness

Yea if you follow this guide, it should allow you to hook up the 1G TT ECU to your harness. Just remember that you will lose your radiator fan so you will also have to wire in a Derale fan controller. You may also lose your AC fan like I did. The derale will also be able to control that.
 

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dumb question because the thread is about connecting 1g tt ecu to 2g harness. But would this work the same if i wanted to use my 2g harness and connect a 95 hybrid tt obdii ecu to it? I goofed up and bought a 99 ecu/harness and now have just learned about its ability to relearn quickly; thus, not allowing me to keep my tune. There's always something you learn while doing the tt conversion ...ah if i could do it over again i could save so much money ;) However, if i could use my na harness with an obdII ecu, would i pass emissions? Damn the enviroment!!! HAHA. Another idea, could i use the 99 harness and plug up a 91-93 ecu since its 3 plug as well? Worst comes to worst i could just disconnect the 02's so i can keep my tune with the 99 ecu, supposedly this works.
 

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Aww wow baby I didn't know you made this!! I'm so happy that you're helping others;) I find that really attractive in a man....
<3
 

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Ok, I have a question. I'm in the middle of my conversion on my 94. Using a 1st Gen TT ecu and my 94 NA harness. The TT conversion car I'm using for the donor has a 1 O2 setup on it. The only o2 sensor is the rear one. The fron O2 Bung has a bolt in it. It's using the first gen tt ecu and harness. Should this work ok?
 

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I would run the two TT O2 sensors because the TT ecu is expecting two signals.
oh yes! I would definitely use both O2 sensors. That is very strange that the donor only had one (could have been its demise) :confused:
 

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Ok, I have a question. I'm in the middle of my conversion on my 94. Using a 1st Gen TT ecu and my 94 NA harness. The TT conversion car I'm using for the donor has a 1 O2 setup on it. The only o2 sensor is the rear one. The fron O2 Bung has a bolt in it. It's using the first gen tt ecu and harness. Should this work ok?
updates TM, you really ought to start a thread.
 

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Mr 3000, Please explain your edit.

**WHEN EXTENDING O2 WIRES, DO NOT SOLDER TWO WIRES TOGETHER! THE SIGNAL WILL NOT READ CORRECTLY! INSTEAD USE CONNECTORS**
I don't understand why that matters. I soldered mine so I need to change mine if it does.

Thanks

btw they have changed the way the fan controller is wired up. I just installed a new one this weekend. I can post up the difference and you can add it to the first post in your thread if you want to do that.
 

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Discussion Starter · #16 ·
Mr 3000, Please explain your edit.



I don't understand why that matters. I soldered mine so I need to change mine if it does.

Thanks

btw they have changed the way the fan controller is wired up. I just installed a new one this weekend. I can post up the difference and you can add it to the first post in your thread if you want to do that.
Yes the only wires that you should never solder together are O2 sensor wires. Why? Well the signal actually gets destroyed by the solder which is really crazy. Yea I didn't figure this one out until after my car broke and the guys up at PCM saw that I had soldered them together. It is actually mostly a little known fact that solder messes up the signal.

I remember that whenever I tried to datalog using the stock O2 sensors, I was getting crazy numbers from them that weren't fluctuating properly and I never could figure out why. So I tuned off of my wideband instead and just had to deal with not being able to verify the results from my datalog. Little did I know that this would still cause problems from time to time because the factory ECU is still reading from those sensors and trying to compensate for what it is seeing and thus my tune would be off a lot of the time.

The way to remedy this is to use crimp connectors. Then once you connect them, wrap the connection so that it can never come loose.
 

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Yes the only wires that you should never solder together are O2 sensor wires. Why? Well the signal actually gets destroyed by the solder which is really crazy. Yea I didn't figure this one out until after my car broke and the guys up at PCM saw that I had soldered them together. It is actually mostly a little known fact that solder messes up the signal.

I remember that whenever I tried to datalog using the stock O2 sensors, I was getting crazy numbers from them that weren't fluctuating properly and I never could figure out why. So I tuned off of my wideband instead and just had to deal with not being able to verify the results from my datalog. Little did I know that this would still cause problems from time to time because the factory ECU is still reading from those sensors and trying to compensate for what it is seeing and thus my tune would be off a lot of the time.

The way to remedy this is to use crimp connectors. Then once you connect them, wrap the connection so that it can never come loose.

It seemed like mine where working correctly (cycling) but also I have always felt like there has been something a little off. It could just be my imagination but anyway I will redo it and see what happens.

Thanks!!!
 

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i am getting to that and i have 1996 CALI-spec and it will be same ?? on body it says august 1995 and title says 1996 and i f i get 1G FED ECU can i use in cali-spec?
 

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i also have a question here. I have a 94 fed spec NA, if i put a TT 94 fed. ecu in the car do i need to change any wires or will it plug right in?
 

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Discussion Starter · #20 ·
i am getting to that and i have 1996 CALI-spec and it will be same ?? on body it says august 1995 and title says 1996 and i f i get 1G FED ECU can i use in cali-spec?
I'm actually not sure about this one. I haven't seen a Stock 3/S ECU in a long time haha. I do remember that the 96+ ECU's didn't seem to be compatible with the 1st Gen's because they had a different number of connectors. I would locate your ECU and find out if you have 3 or 4 ECU connections before proceeding any further. Also, due to the fact that you have a Cali Spec, I would err on the side of safety and go with a Cali ECU.

i also have a question here. I have a 94 fed spec NA, if i put a TT 94 fed. ecu in the car do i need to change any wires or will it plug right in?
No, this will not work. 94+ TT ECU's have 4 connections. Your harness only has 3. The only ECU's that are compatible that will allow minimal modification are the 91-93 TT's. Also, make sure you grab a Fed Spec
 
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