Brake lights work if pedal pressed from outside not inside... (2006 Tahoe Z71)

[fire adept]

Got a pretty weird situation going on with my brake lights that I can't seem to figure out. Noticed I had no brake lights while driving. Got to looking into it and ended up replacing the brake light switch thinking that was gonna be it. Also put in 2 brand new bulbs. Still didn't fix it. So I got to messing around and found out I can get the brake lights to work if I am standing outside the truck and press the pedal, but if I am sitting in the driver's seat (door open or closed) they will not work. Again, they will 100% of the time come on if I press the pedal from a standing position and reach my foot in and press, but if I'm seated in the truck they will not. I've asked around friends and mechanics alike and nobody seems to know whats going on. I've tried unplugging the 2 wiring harnesses in the front of the power seat and the 2 in back and that did nothing. I see some other connections right in the middle of the seat I can't get to without loosening the seat up. I'm just thinking some sort of sensor in the seat or something else, I'm really at a loss here guys. Any suggestions?

 

[OR VietVet]

Welcome to the forum from Oregon.

I have an 05 Z71 and will be looking in to this.

 

[OR VietVet]

Does the wiring harness for the stop light switch and the turn signals travel under the carpet to the rear of the vehicle? I am also curious how the brake lights do when the turn signals are on? The brake lights have to work with the turn signals on. I am curious about maybe a ground being broken when sitting in the seat? I am just seeing what sticks here.

 

[nonickatall]

That sound really weird. You have the same conditions when trying? Engine running, car in park, door open?

I don't know how the brake light switch looks like but when you swapped it, is it possible that the ankle of pressing the brake pedal from inside straight and from ouside in an ankle causes this? For example when there is side play in the brake pedal and the switch i not engaged is a certain position?

Did you try to let someone sit in the car, while phushing the brake pedal from outside, to see if the weight on the seat causes this, which i can not believe.

But as we say in Germany. I've seen horses puke in front of the pharmacy.

Otherwise it is a case for mr. multimeter.. i would measure on the break light if you miss voltage on positive, or mass on negative. Then i would messure resistance from brake light switch to break lights, especially when someone sits on the seat.

 

[Joseph Garcia]

^^^^^x2^^^^^

It appears that force from different angles on the brake pedal results in different results. I'd recommend looking very closely at the brake switch on the pedal where it contacts the brake pedal arm for proper alignment, and the connection of the pedal to the truck body to see if there is any unusual play from side to side.

 

[Doubeleive]

sounds like brake switch alignment, they do move by hand, mine on my 00 would from time to time drop down a hair and I would have no brake lights if I reached up under the dash and moved the switch up it worked again, piss ass design....

 

[Doubeleive]

and as far as I know there is no wire that would affect brakes under the seat, all the stuff under the seat is the SRS module or electrical controls for the seat
the brake light harness should go up and thru the firewall into the main harness under the body along the frame to the rear.
the wires along the drivers side under the kickpanel are to the rear speakers and rear door locks

 

[OR VietVet]

and as far as I know there is no wire that would affect brakes under the seat, all the stuff under the seat is the SRS module or electrical controls for the seat
the brake light harness should go up and thru the firewall into the main harness under the body along the frame to the rear.
the wires along the drivers side under the kickpanel are to the rear speakers and rear door locks

If that is the case, on the harness routing, then I also lean toward the misalignment theory. I did try my 05 and had no problems though.

 

[Doubeleive]

If that is the case, on the harness routing, then I also lean toward the misalignment theory. I did try my 05 and had no problems though.

I bet the side force of pushing it from outside makes it work, but striaght forward it's not touching, you can move them by hand "a little"
probably needs to look up under there with a flashlight for a closer view

 

[OR VietVet]

I bet the side force of pushing it from outside makes it work, but striaght forward it's not touching, you can move them by hand "a little"
probably needs to look up under there with a flashlight for a closer view

I did that on a 1985 F150 that I worked on about 6 months ago. I installed a new switch with a brake booster replacement. I went to check lights and they were stuck on. I adjusted the switch just a hair with my hand and no further rpoblems.