I have done a search on here trying to find a way to determine a fault I have in my backup lights. i have an 86 4 sod so the backup switch is on the shifter.

I am currently rewiring a mess of taillights and other back end wiring on my 308 replica. The PO hacked the wiring pretty badly so I am now tracing wires to confirm what goes where.

I have found that my backup lights have constant power to them. I unplugged the switch at the gear shifter and still have power to the light green wire from the switch plug to the lights. I had the power off and confirmed continuity from end to end on the wire as well as at the C500 connector when apart.

When I took the C500 plug apart I found I did not have power in the wire. Any ideas on how the C500 might be supplying power to the backup lights when all plugged together?

I am at a loss right now..... I will go ahead and trace the rest of my worse back there while I hopefully get some answers here.....

Thanks
Don

Another thought. Does anyone have a pin out for the firewall pass through? I have tracked three green wires there but can't seem to confirm which one is the backup wire. One of the green wires looks like it has another wire going through in the same place so wondering if maybe chafing might be giving a connection? Doesn't quite make sense when I don't get power on both sides of the C500 connection so maybe not. Would be good to have a pin out/location diagram anyway while I am tracing wires.

Thanks
Don

From the 86 FSM, enjoy.

Thanks Seajai;

I went into the C500 block and found that the C1 wire (Dark Blie) is connected and runs into the engine harness but I can't find a plug over by the transaxle that would be for the reverse on a 5 spd. Is the plug there in all Fieros like some other options or is there different engine/trans harnesses for 4 spd vs. 5 spd?

I am still not sure where I am getting the power in the light green line from. I may been to cut into the harness and trace the line all the way end to end to see where it might be chafed or something..... Very bizarre.

Thanks for the pics.

Anyone have the locations of the wires going through the firewall pass through? I think that might help me in my search.

Thanks
Don

Edit: I just had another look at the C500 diagram above and there are 3 wires for backup lights: C1, E1, and F9. Two are light green and one dark Blue. Does the second light green on the engine harness side of the C500 come from the transaxle switch?

[This message has been edited by 355Fiero (edited 09-11-2014).]

There were 2 different wiring harnesses for the 4 and 5 speed tranny models up until midway through '86 (or so I've read). I know this is a long shot, but I remember back in the 70s when I was living in North Van I had a friend who's reverse lights were on all the time. I pointed it out to him and we figured out he had connected the power for his tape deck into the reverse lights, so whenever the ignition was on, it completed the circuit. Perhaps the PO added something in the cabin that required power and tapped into the reverse lights.

Unplug the engine harness and the rear light harness from C500. Then plug in only the rear light harness, Key on do the rear lights come one? If so then you know it is the wiring in the engine harness that is causing the lights to be on.

On some MT Fiero harnesses there is a plug for the reverse light when you have a 5 speed transmission. The plug is located on the branch that runs past the alternator, to the VSS and then to the reverse light switch. If these wires are shorted together (and not to ground) then your engine harness will cause the reverse lights to come on. - So IF IF the reverse lights come on when the engine harness is plugged in (key on) but don't when the engine harness is unplugged (key on) then starting at the VSS start unsheathing the engine harness till you come across the Lt. Green and Dk. Blue wires and then tape them so neither connects to anything.

The connector for the reverse switch will have a Dk Blue and Lt Green wire to it.

The two wires need to be not connected together and not connected to anything else.

quote Edit: I just had another look at the C500 diagram above and there are 3 wires for backup lights: C1, E1, and F9. Two are light green and one dark Blue. Does the second light green on the engine harness side of the C500 come from the transaxle switch?

C1 - Dk Blue - Key on power from the fuse box. Runs to the engine harness and that connects to the reverse switch.
E1 - Lt. Green. - Runs to the engine harness - Gets connected to the Dk. Blue when the 5 speed transmission is in reverse.
F9 - Lt. Green - Runs to the reverse lights. Rear light harness. (Not the engine harness)

Under C500 you will find the Lt. Green from your console reverse switch connects to E1, which also has a jumper that connects to F9. So electrically all the Lt. Green wires are connected together when both plugs are in C500.

See the above diagram if you are confused about the Lt. Green wires.

[This message has been edited by phonedawgz (edited 09-12-2014).]

Excellent. Thanks phonedawgz. I will check that out next week when I get home. I keep thinking this feels like the transmission wires are shorting or something.

Thanks all.
Don