brake Lights Not Working
 

Like the title says....

2002 GMC Jimmy SLS 4x4

So about three weeks back I get a driver up beside me at a stop light who informs me I have zero brake lights. I pull over and check and yeah, nothing.

So put in a new fuse and then I had the top center one working. Took the risk, drove home, picked up new bulbs and installed when I got home.

Happy happy happy - I have all three brake lights working.

Today, again at a stop light, a driver points out I have no brake lights. Get to work, do a test - the center one is working, but not the two side ones.

So, plan is to put in a new fuse, clean the connectors and install new bulbs.

Anything else I should be looking at or plan on replacing?

Thanks in advance folks,
Scott

Update...

New fuse and new bulbs installed.

Interesting thing.

If I lightly touch the brake pedal or push it in just a bit the top brake light lights up but not the side ones. If I bury the brake pedal everything is nice and bright all the way around.

Suggestions?

So all three brake lights work now, you just have to mash down the brake pedal? If so then the brake switch at the pedal is suspect and can be tested easy enough. The top brake is fed by a different circuit, two white wires exit that switch for both legs. Hot is orange. While your down there measure the voltage on orange. You can also test the circuits by jumpering orange to the whites. Also, everything has a common ground G450 left year body. This should be inspected. The two lower brake lights route through the multifunction switch so we need to keep this in mind as well. We’re any of the fuses ever blown? If so, we will be looking for a short as well.

George

Follow up as the truck has been parked until the new camping adventure season starting this month.

Installed a new back switch (on the brake pedal under the dash - AC Delco brand). Still nothing and I would say the top center light is no longer doing anything regardless of how far in the pedal is pushed.

Any suggestions to what I can try next?

Am almost at the point of taking it into a dealer to see if they can fix it, but I just know they are going to hammer me price wise.

What are the symptoms in detail?

George

Started out realizing I had no back brakes lights.

So, installed a new fuse as I figured no way you loose all three bake lights at once.
Once I got back into town, I stopped and grabbed new bulbs (for the sides). Installed and things looked good.
Few weeks go by and I notice no brake lights again, check bulbs and seeing as I have extra install two new ones and hell, lets put a new fuse in as well.

It was then I discovered that if the brake pedal was pushed in all the way, all three lights worked. A light touch on the brake pedal and only the top center light worked.

Did some research, things pointed to the brake switch (under dash). Installed that today.

Currently appears I have no brake lights no matter how far I push the pedal in.

Hazards work fine.
Tail Lights work fine.
Turn indicator lights work fine.
Back up lights work fine.

I'll pull the lower dash off tomorrow after work and confirm the leads to the brake switch are seated fine, but they did look good before I clipped it back into place.

It's been suggested maybe a new combo/multi-function switch but that is out of my roundhouse to install myself.

Thoughts?

Do you have and know how to use a digital voltmeter?

George

Yes and Yes.

Power for the brake lights comes from the "stop lamp fuse (20a) in the UHFB so check that first.

Then that power goes to the stoplamp switch on the brake pedal support bracket.

When you depress the brake pedal switch power goes to two different circuits:

1. The multifunction switch and then on to 4 different fuses and then the left and right brake lights as well as their respective trailer wires. Check Lt turn fuse (10 A) and Rt turn fuse (10A) in the UHFB. Then on to the rear brake bulbs, then ground
2. The output of the brake switch also goes to two fuses and then the center mount high brake light and then ground, the cruise control module and the appropriate trailer wire, all without using the MF switch. Check the vehicle CHMSL fuse (10A) in the UHFB.

If all those fuses look OK then we start testing the voltage and grounds on some wires.

George

As it is, I did take photos of the UHFB today as someone had mentioned to check the CHMSL fuse....

It appears looking at mine, I have nothing in there. I do have a bunch of new fuses, so I take I should pop one into the CHMSL slot? For the record, my Jimmy has the silly LED bar for the center brake light.
For the CHMSL is it just one of the little red 10 A fuses I drop into place, or do I need to buy something else?


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