1990 Buick tail lights stay on

[Egg_Head]

As stated, this is an intermittent issue. Turn off car and sometimes the rear tail lights, not brakes lights, will be lit. This occurs regardless if I have been running the headlights. Occasionally, re-cranking and shutting off will work but I have also observed they will come on a few moments after. Pulling fuse works of course but that's a PITA. Any ideas? The A-body.net forum is closed down and used to be my go-to for tricks.

 

[i6pwr]

I know you said tail lights, but check the brake lights. Why would the tail lights be on and not the headlights is my question.

I believe there will be a switch on the brake pedal. The switches are generally very sensitive and take only a small amount of travel to activate. Might just need re-adjustment, or a new switch.

See if the brake pedal sags when pulled back and let go, could be a weak spring.

What kind of Buick? Likely doesn't matter.

 

[SC Maintenance]

Sticking relay? Only thing I can think of on that vintage that would fix itself during a power cylce?

 

[i6pwr]

Maybe your 3rd brake light is out and it looks like the taillights would be on?

Sticking relay? Only thing I can think of on that vintage that would fix itself during a power cylce?

Wouldn't that control the front parking lights as well? I don't know, just asking.

 

[Sayjac]

The fact that you emphasize, "tail lights" not brake lights has me stumped. Fixed a "brakes lights' stay on issue, on a neighbor's older Civic last year. There it's just a small plastic stopper/plug that breaks and allows brake switch at pedal to stay on.

Watching some youtube electrical repair guys, tracking down a wiring diagram or having the wiring traced down might be needed. Be nice if it was as simple as a bad relay as mentioned by another member.

Let us know with follow up if you get to bottom of it.

 

[i6pwr]

The fact that you emphasize, "tail lights" not brake lights has me stumped. Fixed a "brakes lights' stay on issue, on a neighbor's older Civic last year. There it's just a small plastic stopper/plug that breaks and allows brake switch at pedal to stay on

That's what I'm thinking as well...if the 3rd brake light is out, it would give the indication of taillights albeit bright.

 

[SC Maintenance]

Wouldn't that control the front parking lights as well? I don't know, just asking.

I would need to see the wiring diagram. Only reason I mentioned is its the only thing I can think of that you cycle power and it quits. I am assuming that GM didn't use some kind of BCM in 1990.

Abviosly could be a short, but again why sometimes and not others.

I would say switch, but he says it happens even when not using the lights.

Time to get out the ohm meter.

 

[i6pwr]

I am assuming that GM didn't use some kind of BCM in 1990

Yeah, I want to think that as well.

I would say switch, but he says it happens even when not using the lights.

Hoping it's the brake lights with a burned out 3rd light giving the illusion it's the tail lights.

Otherwise it could be a deep dive.

 

[Egg_Head]

Consulted my Haynes Repair Manual wiring diagram. Looks like the tail lights are "hot at all times" and straight off the light switch. Will start there ...

 

[Jetronic]

It's not switching ground, is it?

 

[SC Maintenance]

It's not switching ground, is it?

How does that work in a car? I understand that from the industrial world, but isn't the entire car one big ground?

 

[Jetronic]

How does that work in a car? I understand that from the industrial world, but isn't the entire car one big ground?

Yes that's the issue. You run the ground wire through a switch or relay (to kill the lights when ignition is off for example) but if that ground wire has chafed it can find another ground intermittently

 

[walterjay]

For a moment there I thought you were driving a Range Rover

 

[SC Maintenance]

Yes that's the issue. You run the ground wire through a switch or relay (to kill the lights when ignition is off for example) but if that ground wire has chafed it can find another ground intermittently

So the light housing itself needs to be insulated then, and the switch grounds it? Sounds like a bad idea. Leads to lights staying on when they shouldn't

 

[Warstud]

Find the headlight/ tailight relay and swap it with an identical one .

 

[Sayjac]

When I watch two of the better youtube auto electric diagnosis techs, most common causes I've seen of electrical issues, rusted/corroded ground wires and connectors, chafed wires and rodent chewed wires. Wiring diagram, a good place to start imo.

 

[Jetronic]

So the light housing itself needs to be insulated then, and the switch grounds it? Sounds like a bad idea. Leads to lights staying on when they shouldn't

the housings are all plastic since forever

 

[Warstud]

Turn off car and sometimes the rear tail lights, not brakes lights, will be lit.

So the headlights turn off but the tail lights remain on and your positive its the tail lights and not the brake lights ?
Now will the tail lights automatically turn off after a few minutes ?

 

[Nukeman7]

Consulted my Haynes Repair Manual wiring diagram. Looks like the tail lights are "hot at all times" and straight off the light switch. Will start there ...

It's not switching ground, is it?

Based upon the statements above, it sounds like the switching ground wire(s) have chafed insulation at a contact point. I'd start visually tracing the ground wire starting from the taillight(s) working forward towards the engine compartment. Focus on friction/bending contact locations such as the door opening thresholds and trunk areas.

 

[CorvairGeek]

These use the 5 terminal, adjustable brake switch used across many car lines. While this circuit is hot all the time, the switch does open and close power, not ground, IIRC.
This body style ('89-'96) never got a BCM and has only about 7 relays max under the hood (the square, Bosch style) on the later, most equipped cars.