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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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GM Sierra 3500: I have a turn signal related problem. Symptoms;

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I have a turn signal related problem. Symptoms; brake applied + left turn signal applied = instrument panel arrow on but no flashing action/sound (freeze). This can happen the other way around with turn signal applied first. Also another situation sometimes; cruise control on + left turn signal applied = cruise control turning off abruptly. These are intermittent events. I have reviewed the electrical schematics found in my 5 volume service manual, and can not find were brake, left turn signal and cruise control have proximity to each other. I have replaced brake and left turn bulbs, and checked a few connections with no effect. I almost decided to buy a turn signal/hazard/cruise switch and replace it, but noticed in the manual removal of other things like steering wheel, SIR disarm, etc. were involved which gave me pause when it looked like only upper and lower trim cowlings needed to be removed, switch fastened and connections made to install this switch.

This vehicle is a GMC Sierra 3500 pickup with crew cab/long box, 6.6 diesel.

Hello and thank you for trusting me with your question. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.

The turn signal and brake lights are on separate circuits. The part on the truck that combines these two circuits into one for the taillights is the Turn Signal Flasher Module. This is located on the back side of the dash fuse panel. Removing the plastic dash panel below the steering column will allow access to the flasher. Replacing the flasher should fix this problem. I have seen this problem multiple times before.

Picture with dash panel removed. #1 is the flasher module.

Customer: replied 3 years ago.

In your answer you did not address the cruise control problem involvement (see question again). Does the cruise circuit also route through the Turn signal Flasher Module?

The cruise control ties into the brake light circuit. The computer must see the ground through the bulbs. Any problems in the lighting circuits will therefore affect cruise control operation.
Customer: replied 3 years ago.

So, just pull module out and put another in with key off. No other considerations?

Thats all. The flasher module simply unplugs and the new one plugs in.


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