No turn signals or brake lights

Chances are the problem is in the turn signal switch. The third brake light circuit bypasses that switch.

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

My guess would be the turn signal switch. A mechanic would check for voltage there.

There is no adjustment. The park lights are on a different circuit than the brake lights.
Do you have a third brake light that works. Its also on a different circuit but works from the same switch. Do your turn signals work. They use the same filament as the brake lights.
Also, the brake light circuit goes through the multi function (turn signal) switch.

Since the brake lights and turn signal lights use the same filament in the bulbs, the brake light circuit will pass through the turn signal switch. When a turn signal is used it cancels out the brake light for that side.

Let me know if your third brake light and turn signals work in the rear.
Also, if youy have not already, check/change the bulbs. The type of sockets those lights are in also get burned so look at them well.

sounds like you have a bad turn signal switch.

If the third brake light is working than we know the fuse is good and the switch is good. The third brake light bypasses the turn signal switch. If the rear turn signals are working than we also know that the wiring from the switch to the rear bulbs is also good. The brake lights and the turn signals are on the same bulb so the turn signal switch is what determines if the bulb gets power from the brake light switch or from the turn signal flasher. If the switch is bad usually the first thing that stops working is the brake lights.

Typically you can wiggle, jiggle, pull, push on the switch lever with you foot on the brake and get the brake lights to work. Sometimes turning the four way on and off several times will also get the brake lights to work. If this is the case than a new turn signal switch will solve you problem.

If you have any questions let me know!

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

The brake light in the rear window and the main brake lights are on a different circuit. After the signal leaves the activating switch on the brake pedal arm, it splits. One circuit goes straight to the high mount brake light, the other goes into the turn signal switch. If the rear turn signals work but the brake lights don't, suspect the turn signal switch, not the bulbs and wires. Better to check this before removing and checking bulbs, wires and fuses. It is a common problem with the W-body cars like Lumina, Monte Carlo, Buick Regal, Olds Cutlass and Pontiac Grand Prix. (Approx 94-99 models). Part number is GM 190005031 (w/o radio accessory control) or 19005032 (with radio controls)

Turn signal switch.

have you replaced the bulbs?

THE 3RD BRAKE LIGHT DOES NOT GO THROUGH THE TURN SIGNAL SWITCH.ASSUMING THE 3RD BRAKE LIGHT BULB IS GOOD.U SHOULD CHECK THE BRAKE LIGHT SWITCH ON THE BEAKE PEDAL.SHOULD BE POWER GOING IN & POWER OUT WHEN U ARE IN THE BRAKE

Turn signal switch 95% of t he time. Try to work your hazards, if it stuck at all will also cause this.