Why won't my turn signal and brake lights on the rear of the truck work


Asked by Apr 30, 2015 at 12:47 AM about the 1986 GMC Sierra

Question type: Maintenance & Repair

rear turn signals and brake lights don't work.  no power in yellow wire all the way to the firewall.  everything under dash works right, looks right, indicator lights work and front lights work fine.

6 Answers


Sounds like the turn signal switch in the steering column. Power for the brake lights flows through the turn signal switch to the rear of the truck. Since the indicators and front turn signals are working the fuse and flasher is good. Do the rears flash with the hazards on? HTH. -Jim

2 out of 2 people think this is helpful.

No they don't.

2 out of 2 people think this is helpful.

Check for power at the light sockets. Both wires are hot (+). One is for the tail lights and the other is for the brake and turn signal. The outer "shell" of the socket is ground. If you have no power there check for power at the turn signal switch. If you have power going to the turn signal switch but none coming out of the turn signal switch. The switch is bad. HTH. -Jim

1 out of 1 people think this is helpful.

Thank you so much! It was broken wires in the steering column. Purchased the new parts today, installed them and we have lights. Appreciate the help. My lighting diagrams never showed the wires for the brakes coming up thru the steering column so I never thought of looking there.

1 out of 1 people think this is helpful.

Awesome!! You're welcome, glad to help. Glad you found and fixed it! Thanks for letting us know. -Jim

1 out of 1 people think this is helpful.

I have a similar problem with my 85 Sierra. My front passenger side and rears don't work. Changed flasher brake switch still nothing. checked current through to rear . I'm getting power to socket but it doesn't blink when turn signals are on. bulbs have been checked and are good. Although when I turn the headlights on the signals cancels out and stays just stationary on the dash . Any suggestions would be appreciated.

4 out of 4 people think this is helpful.

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