I have a few questions on the C500 connector and where to wire some of the wire. I have a 1988 GT swapping in a 2007 series 3 NA 3800 and 2007 4T65E-HD tranny.
I'm using the PCM wiring pinout for a 2004 Impala, and I'm using Dan's 3800 wiring harness tutorial.
Here are my questions please chime in if you know the answer to any of these. Thanks

1. I have a wire in Pin A1 but my 88 service manual says it's not used, I find on the web Pin A1 is the Truck Release Feed if this is correct where do I wire it to?

2. (A4 is for starter ignition on auto tranny cars this wire goes to the neutral switch on the tranny)
OK this yellow wire is huge around 10 gauge wire, all the wires on the round 20 Pin tranny connector are tiny 22 gauge wire, none of which are labled neutral switch, so where do I connect this huge wire?

3. B1 Starter and Charging System. What does this connect to.

4. B3 is from the charge indicator on the gauge pod it can either be connected directly to the alternator pin L or to the PCM C1 pin 36 then PCM C2 pin 61 connects to the alt pin L. Going through the PCM just gives the PCM control of the alt charging.
I believe these instruction is for a different setup then I'm using as my 2007 3800 Stock Alternator connector has a wire in Pin B for Generator Turn On Signal, and pin D for Battery Positive Voltage, no Pin L, My PCM C1 pin 36 is not used, but C2 pin 61 is the generator turn on signal. I can find any other pic on C1 or C2 PCM connector that would be what C1 pin 36 is for.

5. C1 is the +12v feed to the reverse light switch mounted on the tranny on auto and 5 speed cars it is connected to the tranny switch pin B on the 4T60E and 4T65E trannies.
ON My 4T65E-HD pin B is the "2-3 Shift Solenoid Valve Control that goes to PCM C1 Pin 44, so do I just tap into this wire or is there another place I need to connect to.

6. D1 is the ground to turn on the cooling fan and comes from PCM C1 pin 6
D2 is the ground for two stage cooling fans and comes from PCM C1 pin 5.
Since My 88 doesn't have a two speed fan do I just connect D1 to PCM C1 pin 6 and leave D2 unconnected? Pin 6 is low speed cooling fan Pin 5 is High Speed Cooling fan, I assume either will make the fan turn at the same speed just want to be sure the PCM turns on low fan first and in the event it decided to go to high speed does that mean if I'm wired to the low that it will shut off???

7. D3 this is the feed from PCM C1 pin 75 to turn on the coolant lamp on the Fiero gauge
My PCM pinout shows pins 74-75 not used I see no pin that fit coolant lamp so dos this mean I wont have a coolant light if the engine over heated?

8. E1 is the return path from the reverse light switch which is connected to the tranny switch pin F on the 4T60e and 4T65E trannies
My Pin f on the 20 way tranny pin connector is "Transmission Range Signal A" which is wired to C2 pin 18, so do I tap C500 E1 into this wire?


I am ok with these connections just listing them in case I'm wrong on anything.
A2 ground connect to chassis ground.
C2 this is the feed from the coolant sensor to the coolant gauge.
C3 this is the tach feed and comes from the ignition module harness connector pin E which will have to be added into the harness on most cars.
E3 is the +12v ignition feed for the ignition module.

[This message has been edited by Fiero_Guy (edited 09-02-2013).]

Pin A1 was only used for power trunk on the 85 models, that pin is used on some other years but not for any thing to do with the 3800 swap.

The ignition wire goes to the neutral start switch that is mounted down on top of the shifter selector on the tranny which is not used on a lot of newer cars so you will need to get this switch from an older tranny and bolt it on. This switch will also have the reverse light switch in it. Pin B orange wire goes to blue wire from C500 and pin E green goes to green wire from C500.

B1 was only used on the 87/88 I believe alt and is not used on the 3800 alt.

The newer alt will have a two pin plug with a red wire and a grey wire the red goes to C500 pin B3 the grey to a +12 volt ignition source. Hope I am remembering this one properly will check and get back to you.

Reverse light wiring goes to neutral start switch to be added see above.

Use D1 from c1 pin 6 and remove pin 5 from the connector and have the PCM programmed to remove the codes for this as well as some other things to keep your check engine light operating properly.

Can try to connect this to pin 75 it might work your coolant light if not keep an eye on your gauge or add in a second coolant sensor to run the light.

Again for reverse light see above.

The rest are correct, keep in mind the 3 pin coolant sensor used in the 3800 that has the temp feed to the gauge is not very accurate with the Fiero gauge and reads way low. For this you can juts use the gauge as a reference or add in a proper coolant sensor to operate the gauge when making your harness. Big problem here is with the stock 3800 exhaust crossover there is not a lot of room for adding sending units.

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DARN Cars now open with
Over 30 years wiring experience between cars and trade as an avionics technician in both Canadian Air Force and civilian aviation.
Over 25 years experience building and modifying cars.
Over 10 years of full Fiero engine swaps and harnesses building and still going.

So if this pinout I found for the shift selector is correct


Then C500 pin A4 is for starter ignition on auto tranny cars this wire goes to PIn G "Ignition Switched Power Feed"? (On The shift select selector all wires are again small 22 gauge wires the yellow C500 A4 wire is the huge 10 or so gauge wire do I need to connect it with the huge 10 gauge wire or can I use the 20 guage wire I have?)

C500 pin B3 is from the charge indicator on the gauge pod it connects to alternator connector Pin B ""Generator Turn On"

C500 pin C1 +12v feed to the reverse light switch it is connected to the tranny switch pin B "Fused Power Feed".

C500 pin E1 is the return path from the reverse light switch which is connected to the tranny switch pin F "Backup Lamp Feed"

[This message has been edited by Fiero_Guy (edited 09-04-2013).]

I think some of what is hooked up depends on if your car was origionally a stick or auto, you don't say. Both wires are there on each of them. Larry

quote Originally posted by trotterlg: I think some of what is hooked up depends on if your car was origionally a stick or auto, you don't say. Both wires are there on each of them. Larry

My car was an automatic.

Some of the cars with the 4T65E as well as last year or so 4T60E trannies that had the neutral start switch on the tranny have ones with large wires to feed the starter and some that are pretty much useless to us had small gauge wires to work a relay so need to make sure you have the right connector. Dan

Bringing this thread back from the dead. On my neutral saftey switch, the plug pictured above does not have as many wires going into it as what is shown. Mine only has about 4 or 5 wires. I'm unsure where to put my black/orange (park neutral) reference wire. Also not sure how to power the reverse lights since my connector does not have an orange fused battery feed wire.

So my guess is that your transmission connector is missing the fat Purple and fat Yellow wires shown here



You need a connector with the fat wires. You will need to go to the pick and pull yard and get one or you can purchase one from me. $25 if you want one shipped. I'll load it with the correct wires. Neutral safety switch wires (2), reverse switch wires (2) and ground. Paypal me at gofast@reddevilriver.com

[This message has been edited by phonedawgz (edited 08-22-2014).]

No mine has the yellow and the purple. I will take a picture now.

If all you need is a wire for one of the positions, and the two fat ones are already there - depin one of the connectors you are not using and re-use it in your transmission connector. Almost none of the transmission connectors have the wire in blue anyways so you aren't going to find one at the junk yard.

If the two fat wire holes of the connector have thin wires in them you NEED the fat wires, so then you will need to travel to the junk yard.

Take a standard paperclip. Unbend one section. Hammer it slightly to slightly flatten the roundness. Undo the secondary terminal retention clip. Slip your tool in the face of the connector and remove the wire, seal and terminal out the back.

If you look at your connectors, ones that look like they have the right terminal. have rear plastic secondary retention clips, and have individual wire seals should work for you. The majority of the unused connectors in the 3.8 swap will have the right terminal for the smaller transmission connector holes.

[This message has been edited by phonedawgz (edited 08-22-2014).]

my plug only has a black, black/orange, yellow and a purple. So That is what I need, another plug from a car that has the reverse wires and others coming from it.

Let me know the length you need and if you want the correct terminals on both ends. I will ship you a 20ga Lt. Green and Blue wire, each with the correct terminal to fit your transmission switch along with the seal on one end and the large terminal on the Green wire and the smaller terminal on the Blue that will fit directly into your C500.

$15 shipped - paypal me at gofast@reddevilriver.com

You haven't said it yet but I assume your Yellow and Purple wires are large, fat ones sized correctly for the starter as shown in the pic.