Lower brake lights not working

2006 PONTIAC GRAND PRIX

237,000 MILES • 6 CYL • AUTOMATIC

VLIXX

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My rear turn signals began to go out, so I replaced them. Soon after, they went out (at the same time) again and my brake lights followed, both left and right simultaneously. My top brake light and my running lights/taillights work fine.

I have heard it could be a lot of different problems; from the turn signal switch to the computer to the brake light ground wire, etc.

I have tried connecting wire from the wires (both black to black and green to green, have not tried brown yet) located at the top of the trunk lid to the wires coming directly from the bulbs, but nothing has worked.

I do not want to pay a mechanic just to find out that what they fix is not even the problem to begin with.

My turn signals work in the front, and, again, my running lights/taillights work fine. When I depress the brake pedal, only the third light on the top comes on.

What do you think could be the most likely issue?

Thank you!

Jun 26, 2017 at 11:51 AM

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HMAC300

AUTOMOTIVE REPAIR CONTRIBUTOR
48,601 POSTS

are the turn signals working in rear? if not it may be the multi function switch is bad or it is a body module problem. you can check the white wire from the switch to body module and see if it is sending power to module and check dark blue wire and light blue wire from body module to see if it is going through. Or a mechanic can scan for codes and see if it is the body module with his scanner. See picture.

Image (Click to enlarge)

Jun 26, 2017 at 12:18 PM

STEVE W.

AUTOMOTIVE REPAIR CONTRIBUTOR
15,146 POSTS

First check the turn/hazard fuse in the dash fuse panel.

Wire wise if the park/marker lights are working it is not a ground issue to the body. Plus both sides failed and they don't share grounds.

Color wise, black is ground, brown is marker/running light, yellow is left side brake/turn, dark green is right brake/turn.

Are the marker portion of the marker/brake/turn bulbs working? Just not the stop/turn filament?
Because the front turn signals work it rules out the turn signal switch, This one does not break the lamp circuits like the older vehicles, it just signals the body control module left/right. The BCM controls the lights directly. As the fronts are working the switch is working. The CHMSL light is working and it uses the same switch to signal the BCM to activate the brake lights.

I would use a test light to check for voltage on the yellow wire that feeds the left light and the dark green that feeds the right light. If nothing on either one it suggests that the BCM has failed.

Jun 26, 2017 at 12:45 PM