Brake light stays on *Solved - bad relay

[williamcstonejr]

Just spent the last two days researching this hoping HJ would not look at it and post a link directly relating to the subject with 30 seconds of posting. Makes me feel really foolish for asking anyway the brake lights have been staying on, I jiggle the pedal it goes out. The last few days I actually had to pull the fuse to get the light to go out. Any way I went and purchased a new BL switch and replaced thinking I fixed the problem to find the same problem today and I had to pull the fuse. I was thinking bad relay but after looking and researching I cannot find a relay in the box or on the schematics. I took the original BL switch apart and it seems to be just fine, anyone have any ideas on this one?

Old BL switch spring seems to work just fine


I dont see a relay in the schematic it looks like the power goes straight from the BL switch to VECHMSL fuse and the TRCHMSL fuse and the turn signal switch then on it way to the brake lights no relay that I can see.
So maybe a intermittent short in the system?


Also in my searches I came across a TSB that pertained directly to me I have these fuses sitting in my garage right now. It looks like it is for the 15 amp only.

Bulletin No.: 07-08-45-002
Date: September 05, 2007
ADVANCED SERVICE INFORMATION
Subject:
Service Alert: Concerns With Aftermarket Fuses in GM Vehicles
Models:
2008 and Prior GM Passenger Cars and Light Duty Trucks (including Saturn)
2008 and Prior HUMMER H2, H3
2008 and Prior Saab 9-7X
Concerns with Harbor Freight Tools "Storehouse" Branded Blade Type Fuses
General Motors has become aware of a fuse recall by Harbor Freight Tools/Storehouse for a variety of aftermarket fuses. In two cases, these fuses have not provided protection for the wiring system of the vehicles they were customer installed in.
Upon testing the 15 amp version, it was found that the fuse still would not "open" when shorted directly across the battery terminals.

How to Identify These Fuses

[HenryJ]

Have you ever changed the brake fluid?

I would look to the condition of the master cylinder and power brake booster. There may be an issue where the master cylinder / power brake booster is not returning to the full resting position and opening the brake light switch.

Check for excessive freeplay at the pedal. Replace as much fluid from the reservoir as possible, then bleed the brakes until fresh fluid is at each wheel starting at the farthest and working to the nearest. Again check the freeplay. If that does not resolve the issue component replacement may be in order.

Off the cuff, I would suspect the master cylinder.

[killian96ss]

If the brake light switch is propery adjusted I would check for a short in the system.

When the brake pedal is pushed down the switch closes the circuit allowing voltage to the brake lights.

If the circuit is stuck open the lights will stay on.

Is there voltage to the switch without pushing the brake pedal down? If not use a test light and find the short or open between the battery and the switch.

Is there voltage on the ground side of the switch with the brake pedal pushed down? If not look for a short or open in the ground circuit.

Steve

[williamcstonejr]

From what I can see our switches do not provide for adjustment. The only way I could see any adjustment is if the pushrod threads onto the dashpot of the brake booster. The only problem with that is I know for a fact I cannot get my hands back there to make any adjustment even if it is possible. That would require me to take the brake booster off to make any adjustment and hope I get it right the first time. I would not have the patience to remove and install five times.

Switch install


I think I will try with the brake fluid first and go from there if needed. The brake fluid has not been changed since I have had the truck so it should be done anyway. Killiam and HJ thanks for the help. I will post the fix when I find it. I ran two day of searches on the internet for this one and It does not seem to be a uncommon problem with the s-10 trucks. The problem is people would ask for help but not follow through with the fix

[killian96ss]

I believe the switch is self adjusting.

It should make a ratcheting/clicking sound when it adjusts itself after installation.

Steve

[Daveb]

I am having the same problem with my CC. I discovered this when my brake lights stayed on all day at work and my battery was dead that afternoon. Did anyone ever get this problem fixed? It seems to be a common problem with S-10s from what I've read on the net. But so far I haven't saw where anyone has fixed it and posted a reply to what the problem was. I also replaced the brake switch thinking that would fix the problem, but the problem returned with the new switch. I have learned a few things about what is going on. The problem is definitely related to the brake switch. It seems to occur when I hit the brakes lightly. Tapping the pedal or hitting it really hard will usually cause the brake lights to go back off. The third brake light doesn't stay on, just the tail lights. Which is wierd since they all are controlled through the same switch, but different contacts. It is the bright element of the bulb that is staying on. The problem seems to occur at both night and day, so the headlights being on makes no difference. The hazard lights will not flash when this is going on, as if you had the brake pedal pushed in lighting up the brake lights. The turn signals will still work when this is going on. I really don't think it is an electrical problem. I think it is a mechanical problem with the way the switch is being turned on (or back off). What I'm really confused about is why the third brake light doesn't do the same thing. The truck is going to the shop Monday morning. I'll keep everyone posted to what the outcome is. Anyone have any more ideas?

[Daveb]

It seems our trucks have a third brake light relay located under the hood. The guys at the shop said they could tap on the relay and the brake lights would go on without hitting the brake pedal. They replaced it and the problem went away. I probably could have fixed it myself if I had a decent wiring diagram. I have the Haynes book, but it tries to cover all 94-04 models. I didn't even see a relay on their wiring diagram. Anyway, I'm just glad to have it fixed.

[HenryJ]

Thanks! That will help the next person!

[okaussiee]

In my case, the third brake light is out and the ones on the bed are on all the time. The only way for them to go out is to remove the fuse.

I, too, replaced the brake light switch with no results. My cruise control does disengage when I tap the brake pedal. This tells me the new switch is good.

How do you identify the relay under the hood? I looked in the fuse panel and there are relays there, however none state for the third brake light.

Mine is an 02..

TIA

Bill

[okaussiee]

Mine, too, turned out to be the relay. Went to NAPA by my house to get one and they hard a difficult time finding it, but they did and it fixed it.

If anyone is interested is it part number AR176 at NAPA. Cost me 19.69 plus tax..

Bill