Brake light issue (Page 1/5)
stevep914 MAR 12, 03:56 PM
Ever since my recent electrical engine stop failure ( which with a lot of help here we solved, being a ground strap problem): my rear brake lights
are on whenever the power is turned on. I have a racing style cutoff switch at the battery which renders the battery disconnected from the car when it is turned off. Turning this on makes the whole car function, but has my brake lights on all the time. I went at the brake light switch at the pedal, and disconnected it, and the brake lights are still on. Wiring on this car is a nightmare, where it being a kit car, a lot of the stock wiring was played with by the previous builder, although most of the wiring harnesses appear to be stock. Looking at the Haynes manual for the brake light wiring, it shows a relay in the brake light circuit for each rear stop light; I am presuming somewhere before the stock harness goes from the connector from the firewall, to the harness to the rear stop lights. I can’t find one on my car. I DO remember, when the other problem occurred, my two rear cooling fans quit working, and were powered through a relay that sat next to the fuel pump relay on the firewall. The connector to this relay was partially burnt. Testing the wires into this relay showed none of them functioning whether the power was on or not. Currently, those wires, being non functioning, are taped off, with no relay where it used to be. Are there stop light relays anywhere in the stock system? As this seems to be the only noticeable variant from when everything worked before the problem, should I be concentrating my search for a solution there? Thanks in advance! This forum and its members are a wealth of information! Steve
theogre MAR 12, 04:53 PM
Ignore Haynes Rag of a book. Has so many problems and several versions too that changes whatever errors.

Year of car and model even has posted before.
GT uses different taillight then others and can matter here.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

sanderson231 MAR 12, 05:08 PM
In 84 one of the three turn/stop bulbs in the back had a relay. No relay on the other two bulbs but power from the brake switch did go through the stalk.

In 88 no relay / no stalk - from the brake switch straight to the bulbs.

Don't know for sure about other years but suspect that 84 is a loner

If you have cruise there are two brake switches; one for the stop lights and one to disable cruise when brake pedal is pushed.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

stevep914 MAR 12, 05:25 PM
Mine is an 86 chassis, 2.8 v6. The relay that used to power the engine compartment cooling fans had a connector that appeared ( by the number and color of the wires) to be for an air compressor. But my car has no A/C. It was still providing power, although not after the electrical fail issue. If there were stop light relays, where would they be located? I really don’t see any.
sanderson231 MAR 12, 07:11 PM

quote
Originally posted by stevep914:
If there were stop light relays, where would they be located? I really don’t see any.



I found a digital copy of an 86 factory service manual, I had buried on my desk top. In 86 there were no relays. The SE models had the power from the brake switch through the stalk to the bulbs. The GT model had power from the brake switch straight to the bulbs.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

olejoedad MAR 13, 08:28 AM
First place to check is brake switch adjustment.
stevep914 MAR 13, 01:30 PM
Thanks for the suggestions! I guess I am going to have to stumble my way step by step ; I hate electrical issues! I doubt it is the switch at the brake pedal; with the connector disconnected there, the brake lights are still on all the time when the battery interrupter switch is turned on.
theogre MAR 13, 02:20 PM

quote
Originally posted by stevep914:
Mine is an 86 chassis, 2.8 v6. The relay that used to power the engine compartment cooling fans had a connector that appeared ( by the number and color of the wires) to be for an air compressor. But my car has no A/C. It was still providing power, although not after the electrical fail issue. If there were stop light relays, where would they be located? I really don’t see any.

Again.... Model. GT? Or Other?

No Fiero have Relays for Taillights except 84 that "Played Tricks" w/ Taillights to have 3 bulbs per side Active as stop/turn.
All others only 2 bulbs per side for stop/turn.
GT has Amber Rear Turn and Turn Signal is wired for 2 more bulbs.

Brake Pedal have often have 2 Switches w/ or w/o cruise. If have unplug all plugs there then Is Not a pedal or switch problem keeping taillights on.

If taillight stop/turn or GT turn is "On" check front turn bulbs too.
If all are On... Likely the Hazard switch is On but has problems and no Flashing.
No flashing could be bad grounds or Flasher is bad.
stevep914 MAR 13, 07:52 PM
Ogre, thanks, I am digesting this…. Today, I unplugged what looks like a stock 10 pin connector on a harness that comes from the firewall, and when connected, feeds a harness that goes to all the rear lights on the rear clamshell. The colors of the wires on each side of the connector are identical. Again , this looks stock. I am trying to determine which wire feeds the current to the stop lights, and which is the ground. I should be able to get the stop lights to turn on by completing a direct -from- battery circuit applied to these two wires off the pos and neg post of the battery- correct? So far I am not having any luck, as there are many pos and neg combinations depending on which wire does what. The connector has pins labeled ABCDEFGHJK. Pins BHJK are plugged with no wires. A is orange, C is light blue, D is dark blue, E is dark brown or black, F is white, and G is light green. Of course none of these make any sense on the Haynes wiring diagram. ( I know, ignore Haynes, but it is all I have got to work with. ) it would be a great start to know which color wire is the feed from the brake pedal switch, and which is the ground. I am assuming all the remaining wires operate the turn signal lights and rear night driving lights. All that stuff works normally, when the connector is connected, except the brake lights are on all the time. I have tried many combinations of positive and negative to all the wires, and so far cannot get the brake lights to come on. And when I plug the connector together and turn the power on, the brake lights come on all the time, whether the engine is running or not. #*€§!
Patrick MAR 13, 08:07 PM
Steve, I don't know if this could be of any significance... but there have been reports over the years of funky taillight behavior when the rear taillight harness ground becomes corroded and/or detached from the frame.

[This message has been edited by Patrick (edited 03-13-2023).]