I got this harness for a 2003 Grand Prix GTP. I didn't took it out of the car. I see it has two connectors for the type you plug into the trany (two big round ones in picture). Why is that? Is one just deleted when converting to the Fiero (will use auto 4t65e)? Which one is kept then? Thanks

Follow wire colors and pin location on schmatics. they will tell ya

quote Originally posted by revin: Follow wire colors and pin location on schmatics. they will tell ya

Ok. So at the end you end up with only once connecor? Tks

The extra round one is used as a connection to the body harness not the trans, make sure you use the one with the correct pins/colors. The trans should also have a 7 pin connector under the select lever, if its not there you will need to add one for neutral safety and backup lights. If yours doesnt have the connector under the lever that also means your trans uses an internal mode switch wired through the round connector instead of the 4 pin that would be next to the 7 pin. Make sure you follow instructions that include the internal mode switch if that is the case.

quote Originally posted by Mike Gonzalez: The extra round one is used as a connection to the body harness not the trans, make sure you use the one with the correct pins/colors. The trans should also have a 7 pin connector under the select lever, if its not there you will need to add one for neutral safety and backup lights. If yours doesnt have the connector under the lever that also means your trans uses an internal mode switch wired through the round connector instead of the 4 pin that would be next to the 7 pin. Make sure you follow instructions that include the internal mode switch if that is the case.

Ok. That's what I thought of the 2nd round one. My transmission didn't come with the connector under the lever but since I bought it from a recycler who knows if he took it out. But my trany is a 2008 4t65E so maybe it didn't come with it. Thank you very much Mike. You always come up to help all of us in the 3800 illiterate camp

Starting in 1999, GM introduced a new feature on the 4T65-E transmission. It was called the Internal Mode Switch (IMS). It performs the same function (for the PCM) as the neutral safety switch that mounted on the outside of the trans over the gear selector shaft. As the years went on, more and more 4T65-E's used the IMS and dropped the external switch.

My information indicates the 2003 Grand Prix 4T65-E would have had the IMS, which means it probably would NOT have had an external gear position switch. Therefore, you may not have the 4-pin connector on your PCM harness for the gear position switch (or even the 7-pin connector that contained the wires for the starter neutral safety circuit and backup lights circuit).

The 2008 4T65-E most certainly would've had an IMS.

It is important to note that the IMS does NOT contain the circuits for the backup lights or the starter neutral safety cut. Those functions would have been handled by the BCM/PCM instead. The good news is GM left the mounting provisions for the external gear position switch on every 4T65-E that I've ever seen that had an IMS, so that means you should be able to install this external switch and wire up your backup lights and starter neutral safety cut without having to install a BCM to control those functions. When I use one of these transmissions in a Fiero swap application, I usually just modify the stock Fiero's neutral safety (and backup lights) switch so I can use it on the 4T65-E; thus eliminating the need to buy a 4T65-E specific switch.

-ryan

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quote Originally posted by Darth Fiero: Starting in 1999, GM introduced a new feature on the 4T65-E transmission. It was called the Internal Mode Switch (IMS). It performs the same function (for the PCM) as the neutral safety switch that mounted on the outside of the trans over the gear selector shaft. As the years went on, more and more 4T65-E's used the IMS and dropped the external switch. My information indicates the 2003 Grand Prix 4T65-E would have had the IMS, which means it probably would NOT have had an external gear position switch. Therefore, you may not have the 4-pin connector on your PCM harness for the gear position switch (or even the 7-pin connector that contained the wires for the starter neutral safety circuit and backup lights circuit). The 2008 4T65-E most certainly would've had an IMS. It is important to note that the IMS does NOT contain the circuits for the backup lights or the starter neutral safety cut. Those functions would have been handled by the BCM/PCM instead. The good news is GM left the mounting provisions for the external gear position switch on every 4T65-E that I've ever seen that had an IMS, so that means you should be able to install this external switch and wire up your backup lights and starter neutral safety cut without having to install a BCM to control those functions. When I use one of these transmissions in a Fiero swap application, I usually just modify the stock Fiero's neutral safety (and backup lights) switch so I can use it on the 4T65-E; thus eliminating the need to buy a 4T65-E specific switch. -ryan

The 2003 harness that is used on my 3800SC series III /4T65eHDswap (2006 engine) had the connector for the external gear position switch. We just added the earlier switch and plugged the harness right in. The 06 transmisson did have the internal IMS switch but we just didn't use it. Everything works fine.

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quote Originally posted by Dennis LaGrua: The 2003 harness that is used on my 3800SC series III /4T65eHDswap (2006 engine) had the connector for the external gear position switch. We just added the earlier switch and plugged the harness right in. The 06 transmisson did have the internal IMS switch but we just didn't use it. Everything works fine.

Might have; not all 2003 4T65-E's had an IMS.

Concerning the pinout of the external gear position switch (if you are using one from a 4T60-E or 4T65-E)...

Large 7-pin connector:

A - P/N signal output (grounds when shifter is in park or neutral; not needed for Fiero swaps)
B - Reverse lights power input (connect this to a key-on 12v + power source; usually pin C1 of the Fiero's C500 connector - DK BLUE wire)
C - not used (connects to pin B when shifter is in park - not needed for Fiero swaps)
D - ground input (for P/N signal and PCM portion of the switch) - connect this pin to ground
E - starter P/N safety switch circuit - connects to G terminal with shifter in park or neutral (connect to Fiero C500 pin A4 yellow wire [AT Fieros] or E2 purple wire [MT Fieros])
F - Reverse lights output (connect this to the LT GRN wire coming from pin E1 of the Fiero's C500 connector)
G - starter P/N safety switch circuit - connects to E terminal with shifter in park or neutral (connect to starter solenoid)

Small 4-pin connector (for PCM connection only)
A - PCM Trans Range Parity Signal output (WHT wire) - [grounds in P, N, 3, 1]
B - PCM Trans Range B Signal output (YEL wire) - [grounds in R, N, 4, 3]
C - PCM Trans Range C Signal output (GRY wire) - [grounds in 4, 3, 2, 1]
D - PCM Trans Range A Signal output (BLK/WHT wire) - [grounds in P, R, 3, 2]

-ryan

on the 4 pin connector what are the PCM pin ID's?

Is this correct and are other thing connected to these pins?
A - PCM Trans Range Parity Signal output (WHT wire) - [grounds in P, N, 3, 1] PCM Pin = C2 16
B - PCM Trans Range B Signal output (YEL wire) - [grounds in R, N, 4, 3] PCM Pin = C1 68
C - PCM Trans Range C Signal output (GRY wire) - [grounds in 4, 3, 2, 1] PCM Pin = C2 56
D - PCM Trans Range A Signal output (BLK/WHT wire) - [grounds in P, R, 3, 2] PCM Pin = C2 18

quote Originally posted by Darth Fiero: Small 4-pin connector (for PCM connection only) A - PCM Trans Range Parity Signal output (WHT wire) - [grounds in P, N, 3, 1] B - PCM Trans Range B Signal output (YEL wire) - [grounds in R, N, 4, 3] C - PCM Trans Range C Signal output (GRY wire) - [grounds in 4, 3, 2, 1] D - PCM Trans Range A Signal output (BLK/WHT wire) - [grounds in P, R, 3, 2] -ryan

Hoping to get a confirmation by the weekend.
Thanks

Remember the chassis ground for the external selector switch was on the neutral start switch connector or it will not work. Dan

Correct.

quote Originally posted by CC Rider: Hoping to get a confirmation by the weekend. Thanks

Thanks guys!