Rear lights all work but not when brake is applied

I can almost 100% guaranty the turn signal switch is the problem. Power for the brake lights starts at the brake switch. power then splits from there and the third brake light gets power directly from the brake switch. Since the turn signal and the brake lights are on the same bulb power for the brake lights is routed through the turn signal switch. the switch depending on what position it is in will allow brake power or turn signal power to there respective left or right brake/turn bulbs.

If you hold your foot on the brake pedal and wiggle the turn signal and or play with the hazard switch the brake lights will almost always intermittently start to work. this will confirm a bad turn signal switch which is pretty common on GM vehicle with this style setup.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

feed supply problem somewhere ?but where ? try checking the wiring loom at the rear or as its called in american "pigs tails"

The first step is to check the bulbs in the tail lights. The brake light switch (on the brake pedal) is OK, as the center light works.

Replace the turn signal switch. All of these lights run threw it.

you don`t say if its both or just one brake light out.you say the light itself is on but not if you mean tail light or what.the tail lights use a different filament in the bulb than the signal light which is the same filament that the brake light uses.if the signal light work on the rear then the bulbs are good,if just one side works then the bulb is no good on the side that doesn`t work.if the signal lights work but neither brake light works then you need to check the fuses in the fuse panel under the dash on the drivers side.if the fuses are good then it will be either a bad wire at the brake switch or a bad brake light switch,this is located on the brake pedal lever under the dash.

Replace the turn signal switch. Bad contact inside causing a crossing of the circuits. When the turn signal is applied it should open the brake light circuit allowing for just the signal to work. Doesn't sound like the switch is doing it's job.

I know what it is. I have the same problem. Try, when pressing the break, pulling your turning signal lever towards yourself, but not all the way to turn on the brights. If your breaks light up then you need a new turn signal switch. Part of the switch disables the break lights when that flasher comes on, but when it goes bad, it wont let the lights com on at all.

I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!

I had the same problem. They were on when the headlights were on, but turned off instead of brightening when I pressed the brake. I replaced the bulb and now it gets bright when I press the brake instead of turning off (like it should).

check fuses