I’m in the middle of swapping out the rear clip of an 88 Formula notchback and putting on an 86 GT fastback clip. The problem I’m having is when I use the wire harness from the GT I have no brake lights. All the other lights seem to work fine. I have look at the connection from the C500 block and the pining don’t seem to match. Do you think I need to move one of my pins or do you think there is a short in the harness?
I swapped a fastback conversion onto my 85GT last fall and ran into that same problem with the brake lights. Yours may be different since you have an 88 and a fastback was offered for your year. I had to run a wire from the brake pedal all the way back to the C500 harness and pin it in there. You should be able to ground out your brake lights and that is where you want to run to wire to from the brake pedal. Hope that helps. Again yours may be different as you have an 88.
Thanks Ken
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10:57 AM
Raydar Member
Posts: 40910 From: Carrollton GA. Out in the... country. Registered: Oct 1999
I have a complete rear lighting wire harness from an 87 GT if anyone is interested just make me an offer. One of the bulb connectors for the light up "PONTIAC" is smashed, but a replacement is a couple bucks at your local parts store or through the fiero store.
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08:59 PM
sthtxfiero Member
Posts: 212 From: rockport texas Registered: Feb 2004
i am helping strick on this car and due to the way the GT turn signals are amber and they are red on the notchback so when you press the brake it makes the amber lights come on because the brakes are on the same circuit as the turn signals? now has anyone repinned inside the C500 to make the brake lights on the same circuit as the tailights?are we missing something can we not see the trees for the forest? i know someone has tackled this job before anyone any suggestions????
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10:55 PM
Jun 2nd, 2004
Indiana_resto_guy Member
Posts: 7158 From: Shelbyville, IN USA Registered: Jul 2000
Well I had to move pin J9 to G7 on the C500 block. I also wasted a few hours trying to get back up lights to work until I final traced it down to a bad Back up light switch.
I've fixed this before. And frankly there is two tail harnesses for these cars. You have to cut the brake wire where it goes up the column to the blinker switch then route it to your harnesses brake lights. This will....
#1 remove the BRAKE signal from the AMBER BLINKERS #2 Bring a BRAKE signal to the back via a new route.
Notch backs have this all together
Fast backs have them separated. Period.
If you have a 3rd brake light you can tie into it for the brake signal but you still have to remove the BRAKE signal from the turn signals by cutting the wire. Only bad thing is I'm not sure hwere the 3rd brake light ties into THAT wire.
Well I had to move pin J9 to G7 on the C500 block. I also wasted a few hours trying to get back up lights to work until I final traced it down to a bad Back up light switch.
I'm converting an 88 coupe and I ran into the same problem. The taillight harness is most definitely NOT plug and play as far as the brakes go because as Stuart Lowery points out the notchies have brake/turn together and GTs are separate.
But here is where I am getting confused. My amber turnsignals are working perfect as turn signals but they are not coming on with the brakes as others have suggested they would. The normal GT brake lights are not coming on with the brakes either. (3rd center high mounted stop light is working normal)
I wish I understood the "move one pin at the C500 solution" a little better. My Helms is a little confusing. It implys the harness is plug and play but apparently not.
Is there anyone who has done this can help?
------------------ If you find my advice useful, then please give me a positive rating, thanks... 1988 GT (Firebird Interior),1988 Coupe (Daily Driver), 1985 SE (Project Car), 1985 Coupe (parts car), Firebird Interior Installation Website
The one in my helms did not match what I had. I used the 88 Service Manual. I have no way of scanning the pages but I will try to take a picture of it and post it here.
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09:57 PM
Riceburner98 Member
Posts: 2179 From: Natick, Ma, USA Registered: Apr 2002
I wish I had my manual with me right now... From memory, I thought they set up the in-car wiring harness to work as both GT and SE versions, and just the taillight harness was different?? From what I remember, there are 2 white wires coming out of the brake switch, or possibly from the brake switch to the turn sig. switch, then they head out to the back of the car. One of them is not used on the SE (OK does this sound right -- One white wire comes from the brake switch, all the way to the C500 connector. On the SE taillight harness, there's a "jumper" or "loop" of wire that sends this "brake only" signal back down the other white wire to the turn signal switch, where it gets sent out on the "turn signal" wires when you hit the brakes. On the GT that brake - only wire does just the brake lights, and does not connect to the "turn signal" wires. ) Man, I almost had that page in the book memorized too, it took me a few minutes to figure out what they're doing there. I was doing the same notchback - fastback swap, but when I decided to throw the 3800SC and the Mitsubishi interior in there, I just re-wired most of the Fiero wiring harness so I'm not 100% sure on what to do with those white wires. Does anyone have a scan of the brake switch / turn signal page from an '86 + book?
------------------ Bob Williams Multi-colored '87 Mutt, a work in progress! (3800SC installation in super-super-ssuuppeerr-slow-motion progress... Done for Kansas? Riiiiiiiight....)
Jscott1, Because of there size I put a link to them below. What I did was on the coupe wiring harness is I removed a white jumper wiring going from G7-H8. Then on the GT harness I traced from my break lights and found a blue wire was pined in at J9. I removed it from there and used the connector from the white wire and pined it in at G7. That fixed all my problem. Lights work great now. Hope this helps.
My Helms doesn't even have a J9, but I went with that and my C500 was so covered with goo to find G7 I just probed all the white wires until I found it. I made up a jumper and instant brake lights.
A plus for you
[This message has been edited by jscott1 (edited 06-03-2004).]
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11:10 PM
Riceburner98 Member
Posts: 2179 From: Natick, Ma, USA Registered: Apr 2002
Wow, I got it right... But I wonder why the stop lights were pinned at J9??? Wouldn't that have made them not work on the donor GT? Wierd... But at least you don't have to run any new wires, just change some pins around at C500. Good explanation Strick. This is a good one for future search engine users to find.
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11:30 PM
Jun 4th, 2004
sthtxfiero Member
Posts: 212 From: rockport texas Registered: Feb 2004
i swore he was gonna give up but he just kept going back to the book the whole time i was saying lets splice it . i told him a lesser man wouldve quit.
Great job Strick! My manuals don't even show that stuff and I have 3 books to look at. I wonder what all years were that way. I'm going to check out my 85 about that.
A plus for you
But I wonder why the stop lights were pinned at J9??? Wouldn't that have made them not work on the donor GT? Wierd... But at least you don't have to run any new wires, just change some pins around at C500. Good explanation Strick. This is a good one for future search engine users to find. 
