I'm currently fixing up a 86 GT with an automatic transmission and I've been fixing the wiring in the engine bay which as we all know can get a little messed up by previous owners.

I was looking at the C500 connection and found a heavy yellow wire, which is the one on the left in the pic below, bypassing C500 and it was actually wrapped around another yellow wire coming out of C500 and wrapped with electrical tape.

I'm guessing the yellow wire is part of the neutral start switch but I'm confused as to why there are two of them.

The purple wire for the circuit can be seen near where the left yellow wire goes into the harness on the left side of C500.

I'm wondering where the yellow wire on the left originally went and where the one on the right coming out of C500 goes.



I've included the wiring schematic for the circuit too.



Any help is appreciated.

If you need clarification on anything let me know.

Steve

------------------

Where will the road take you today?

Some helpful links I've done
How to remove inner door panels, with pics.
How to remove outer door panels, with pics.
How to make rear coil-overs using factory struts, with pics.
How to remove rear bearing hubs, with pics.
How to modify the stock Fiero radio for MP3 players, with pics.
How to come up with the right coolant hoses for that engine swap...With Pics.
Basic Fiero electrical testing "How To" and equipment...with pics.

The one on c500 should be at pin A4 it is your "crank" wire,. goes to the trans neutral safety, from there the "crank" wire is purple to the starter. The on on the left im not sure about yet.

Any chance the car was converted from a manual shift? (I am doing that) I haven't gotten to that part yet but I was told there was something like this (yellow and purple wire) that I will have to do to get it to crank. I have the info at home somewhere.

As near as I can tell the car has always been an auto.

I'm going out to work on it now and will try to trace where all the wires yellow and purple go and come from.

Steve

Here is the 86 C500 pinout diagram - should help you some (funny it does not indicate anything in A4 - this is right from my 86 FSM).

[This message has been edited by Mickey_Moose (edited 03-09-2009).]

OK, I did a little digging and wish I had done it last night but I was tired.

Here's where the mystery yellow wire goes, it splices into the purple wire before C500.



Now here's a better shot of the yellow wire that is attached to the C500 engine harness connector.



Now from what I can tell using this C500 pin out from the 86 service manual the yellow wire is in the A4 position and according to the pin out the purple is in the E2.



So I would have to guess the engine was swapped out with a non-86GT V6 and as the yellow and purple were not connected they were bypassed.

Luckily the splice was just wrapped around the wires and not soldered.

Guess I'll pull C500 apart and move the yellow wire.

Thanks for the help.

Steve

If you remove the C500 plug the pins are marked along the sides (molded into the plastic) - letters down one side and number down the the other. That way you know if you have the correct pinouts.

If I had to guess right now, looks like someone modified it to bypass the gear selector switch.

From my experience, the C500 engine harness is the same from 86 and up. There is a wire difference in the 85 motors (and well the 84, but that isn't even close (not counting that it is a 4 cyl)).

Cheers,

[This message has been edited by Mickey_Moose (edited 03-09-2009).]

Thanks, I looked at the pin out for the 85 C500 and it has the A4 as the yellow wire so it looks like someone did a swap from a 85 V6 to this 86 GT.

Guess I'll have to do some more digging.

Steve

[This message has been edited by fierohoho (edited 03-09-2009).]

well, my 88 FSM shows A4 in the C500 diagram, so the diagram in the 86 book is probably a missprint.

As I said, there was probably a problem with the selector switch and the previous owner just bypassed it so that he could start the car. Verify your wire when compared to the schematic you posted in the first post and you should be good. That is to say the key switch connects to C500/A4 via a yellow wire (probably the backside of the connector), this wire then leaves the C500 (engine bay side of the connector) and feeds the gear switch's input. The output of the gear switch is the purple wire that feeds the starter. Easy to test, use a volt meter connected to A4 (and ground) - turn the key one, you have 12v (or there abouts), key off nothing. Gear select switched bypassed due to the yellow wire connecting to the purple wire directly.

According to the diagram, if the car is an automatic C500/E3 is not used, if it is a standard C500/A4 is not used. The wiring harness may have both sets of wires as it was probably easier to GM to make 1 harness for the car vs 2 different ones. I know my 86 car had the wiring in place for both the Izusu tranny or the 4 speed.

Since your car is an automatic, ignore the wiring on the right side of the diagram (cover it up as it does not apply to your car) - the diagrams is just showing this is the wiring for an auto OR this is the wiring for a manual car.

Hope that kind of makes sense...

Thanks, that makes sense and confirms what I was thinking.

I'll get back to it tomorrow and let you know what I find out.

Hey, at least it started and idled pretty good with the bypass.

Steve

Well I did some more diagnosing and here's what I have.

I'll start at the ignition switch.

There is power at the ignition switch from the fuse link.

The yellow wire leaving the ignition switch has power when the key is turned to the start position.

The Park/Neutral Switch at the transmission is good.

The yellow wire between C500 and the Park/Neutral Switch is good, no breaks.

The purple wire between the Park/Neutral Switch and the "S" terminal on the starter is good, no breaks.

If you apply power with a jumper to the purple wire as it leaves the Park/Neutral Switch the engine will turn over.

There is no power to the yellow wire that goes from C500 to the Park/Neutral Switch when the ignition key is turned to the start position.

The purple wire that goes into C500 gets power when the ignition key is turned to the start position, (this is where the yellow wire on the left is spliced into as can be seen in the first pic in my initial post).

So my issue as it stand now is there is obviously a problem between where the yellow wire leaves the Ignition Switch and how it gets to C500.

I will next trace the yellow wire from the Ignition Switch to C500 and I wonder if I won't find that it changes to a purple wire somewhere along the way which would mean the service manual is wrong and my issue is at the C500 connection.

Any new input is appreciated, thanks.

Steve

Unplug the C500 connector and measure if you have voltage with the key in start on the plug (the side that is attached to the frame of the car). If you have power there, then the problem is in the C500 (pins not making contact). edit: now I don't recall, but if the C500 is unplugged you might not get any power there even it is good as it might be a power feed as well - worest case you can always stick the tip of your prope through the insultion on the wire on the backside of the plug.

If no power, remove the console, find the yellow wire in the bundle on the passenger side. Push the tip of you meter's probe through the insulation and test for power here. If none problem is between the switch and this point and I would suspect dropping the column and checking the connections around it. If you have power under the console, you might as well start with the cuss words now because that part of the harness is a bear to get it with the engine in the way, but start by testing the yellow wire in the engine bay side right at the bulkhead pass through (the rest is all taped up and such) - check the harness if it looks like it was rubbing at some point or pinched. Best way to check wiring is first from each end, split it in half and test there. The wires themselve are probably ok, it's more like an issue near one of the connectors (unless the harness was pinched at some point).

[This message has been edited by Mickey_Moose (edited 03-11-2009).]

Thanks Mickey_Mouse,

I've done a little more digging and here's what I found and what I think.

There is no yellow wire, (sized like the ignition wire), that goes through the bulkhead connector on the passenger side by the ECM.

There is a purple wire that goes through there and it does get power when the ignition key is turned to the start position.

Looking at the wiring diagram for the starter you will see a factory splice, S207, this is where I believe the wire changes from yellow to purple and the color from there to C500 is wrong in the diagram.

I can find no other explanations and feel that the engine and harness were switched out in the past which is why the yellow is at A4 and the purple is at E2.

So, I have C500 apart and I'm going to switch the yellow wire to the E2 slot.

Can someone tell me how to release the yellow wire from the engine harness connector?

I've been playing around with an old connector but I'm not having any luck and don't want to force anything.

Thanks,

Steve

That is what I was talking about in my post earlier. It sounds like you have an engine harness from a manual and an auto harness in the car (or vice versa). Mine was a Manual shift car I converted to Auto.

This was sent to me by Ed Parks at the Fiero factory:

At the C-500, you will see the heavy gauge purple wire in a cavity from
the cabin harness side. But, the auto engine harness will have a heavy
gauge yellow wire in a cavity that does not match. You will need to have
both the purple and yellow in a cavity across from each other (you can
move either). That will complete the starter circuit.

Thanks Terry,

From what I can tell it was always an auto car, I'm pretty sure the motor and harness were from a 85 with a manual.

Any tips on removing the wire?

Steve

sounds like someone had trouble with the park/neutral switch, and went and bypassed it. OR - someone added a 2nd "no start" switch somewhere?

anyways - the test: put the car in gear, and see if it starts. I am guessing it will.

if it does not - search the car for a secret switch, which shuts off the starter

I got sidetracked on another Fiero, so I have not moved the wire yet. If you do move it give me some pointers. I guess the only way to be sure about the car always being an auto is to check the numbers. When I swapped mine out I moved everything. I don't think anybody could tell it was swapped by just looking at it (except I chose to leave the clutch line in place (at least for now).

After thinking about it (I have never had a manual shift engine harness the car I bought was missing the drivetrain), it doesn't make sense that the engine harness is manual. I am assuming the connectors are different on the transmission. So unless the car was a manual at one time I doubt it was the miss match. I still believe the yellow and purple wire need to be connected. Maybe the PO thought the connection was bad so he was trying to bypass the connector by splicing them together. If the connection was the problem it should work and would not affect the neutral switch.

Well something got switched before I got the car so I'm moving the yellow wire from A4 to E2 which should fix the problem, well at least that problem.

Steve

Well I got the yellow wire switched and I put C500 back together and all is well for "that" problem.

Just thought I'd post a few pics of how to remove a wire from the engine harness side of C500 for those that are curious.

Here's the connector.



If you clean the dirt and crud off the end you will see a white strip like this.



Pry it up with a small screw driver.



Here is the white piece removed, it is used to lock the wires in place.



Just an FYI to close out this thread.

Thanks for the help everyone.

Steve