Break light issues

adawson00 · February 25, 2013

1990 GMC Sierra 1500
3 days ago, I started my truck and the "brake" light was on on the dash, i tried pulling to release the parking break and it wasnt engaged but the light wont turn off. Now I have no break lights when i push on the breaks. I checked the fuse and its good. I think its the bulbs but everyone tells me its not cuz the chances of them both going out at the same time is unlikely. Any ideas as to what it could be and how to fix it?

citydriver · February 25, 2013

Do the hazard/turn signals work? If so, it's not the bulbs. I'm trying to remember if there is a relay inline for the brake lamps, but I'm not sure about that. Your best bet would be to get your hands on the electrical diagrams for that model year ( Hanes Manual, Chilton, Alldatadiy.com, etc..) and trace the circuit. It's been awhile since I had my '88 or my '91 so I can't remember clearly. You can also check for power at the brake light switch located on the brake pedal under the dash, one wire would be "HOT" +12v, may be ORANGE if I remember right. The other wire will have no power to it until the brake pedal is pushed. That wire may be WHITE and goes to the turn signal switch, which is part of the brake light circuit. If the brake light switch is operating correctly, I have seen the turn signal switch be bad or a break in the wire somewhere in the steering column ( especilly if it's a TILT column ). A 12 volt test light and a wiring diagram would be your best start, the above are only my best guess'. As for your BRAKE warning lamp on the dash, It could be low brake fluid level IF there is a sensor in the reservoir or a fault in the rear wheel anti lock brake system ( if it is equiped with one ) This is also where a vehicle repair manual comes in handy to help with diagnostics. I use http://www.alldatadiy.com/index.html , or you can pick up a decent paper manual at your local parts store.

adawson00 · February 25, 2013

I checked my hazards this morning and they didnt work. So does that mean its the bulbs?

citydriver · February 25, 2013

What about the turn signals? It may be the bulbs, it is possible that the bulbs went bad, at or near the same time. It's rare, but I have seen it happen. Heck, one of them may have went bad the day before the other without you noticing. It's only a couple of screws that hold the tailights in, wouldn't take long to check....