SureTrack Real Fix: Bleeding Lights

Bleeding lights? What could that mean? SureTrack community member Bellis@Grrrsafety had a GMC Pickup in their shop that had a problem with lights turning on when they shouldn’t. They posed the question to the community, and with the help of fellow community member WALKERAUTOREPAIR and others, they were able to resolve the issue.

The following Real Fix summarizes the interaction between them in the community that led to the solution.

Vehicle
2003 GMC Sierra 2500 HD 6.0L

Title
Left Turn Signals Inoperative, Replaced Turn Signal Flasher Module

Complaint
Left turn signals inoperative front and rear. When brakes are applied the left turn signals/markers light up on front and rear.

Diagnostic Steps Performed/Parts Replaced
Searched wiring for possible shorts, found none. Isolated rear lights controller and checked for brake bleed to front light, no change. Checked fuses and didn’t find any related bad fuses. Disconnected brake light switch and checked for operation of turn signals on left with no change. Removed rear light bulbs to see if the filament was crossing and didn’t find anything there. Disconnected snow plow diverter box and had no change. Is there a light control box that could be bad or what would you check next? I’m running out of things I personally know to check. Am I missing something and is this a common problem?

Best Answer from Community Member WALKERAUTOREPAIR
I had this happen and it was the turn signal flasher module. It is sold after market.

Cause
Thanks everyone for all your help I would not have figured it out otherwise. I had taken the flash control unit off and checked to see if it still did it and it did not.

Correction
Replaced turn signal flasher module (control unit), problem resolved.