1998 gmc Sonoma brake lights

The brake lights on my truck are not working all the fuses are good, the bulbs are good, I have changed the brake switch. They still do not work, altho all the other lights at the rear work even tail lights. Idk im confused

Does the high center brake light work?


Somewhere else on this forum there’s a thread lamenting things like brake lights that are controlled by the body computer and wishing that things were simple again like on your truck.

If your turn signals work but the brake lights don’t and you’ve verified power at the brake switch and/or replaced it I would suspect a faulty turn signal switch. But I would consult a wiring diagram and test to be sure.

Try cycling the emergency flasher switch to see if that helps. If the middle brake light isn’t working then there may be some other trouble. You should verify that power is getting to the brake switch, as was mentioned previously.

There is power to the brake switch but nothing to the lights. But there is clicking coming from under the dash.

The third brake light hasn’t worked since I bought it but I didnt care about that

Since you have proven that power is getting to the switch then the most likely suspects for the problem is the emergency flasher switch and the turn signal circuit. The brake circuit has to pass through both of those circuits I believe. See if the emergency flashers work and if so then I suspect that switch is where the problem is at. Cycling the switch a number of times may clear the bad contact. The middle light most likely has burned out bulbs in it and you should check them.

Ok thank you im going to check that I changed that hoping to fix the headlights but seems I caused more problems

Switch, then turn signal switch then stop lamp.

Make sure that all 3 stoplight bulbs have a good ground. My wife’s 2003 Blazer had this exact problem. I ran a new ground and all brake lights started working. If you check for voltage assuming the ground is good…you can get a zero reading.

there is no power getting to the rear brake lights . Im about to check the third light

Im lost on this truck every since I bought it its been wiring issue after the other.

Try turning on the emergency flashers and see lights in the back work then.


Ok third brake light works fine now I replaced the bulbs but still no rear brake lights

You need a turn signal/multifunction switch.

The high center brake light circuit doesn’t pass thru this switch, but the regular brake lights circuit does.


How are you determining there’s no power at the light switch? You have to measure using two test points right, one the power and one the ground. Are you using a known-good chassis ground for the ground test point?

@Tester … I see what you mean by looking at the schematic posted above, just wondering what the manufacturer’s motivation might be to run the brake light circuit through the multi-function switch? Is it so they can use the same bulbs for both the turn signal function and the brake light function? Save on parts count and reduce the amount of wire needed?

It serves three functions.

Turn signals, brake lights, and emergency flashers.


I use a test light with a very good ground. I have now pulled I the dash and…I am looking further into this problem. As I said before there is a clicking noise coming from under the dash

I still have all lights but brake lights