Replace the switch.
Power is being interrupted; the turn signal switch is a power juction see if the power is flowing thru it.
A brake light switch is a mechanical electric switch that is set in the off position (open circute) and located in front of the brake pedal. When you step on the pedal and its position changes the switch complete's its circute sending power to the brake light. The brake light switch is protected by a fuse or circute breaker and has no other connection with the operation of the brakes.
Check to make sure you have power at the brake light switch, if you have power at the switch, depress the brake pedal, and check for power out of the switch, if no power out with the brake pedal depressed, you need a new brake pedal switch.
The 1996 GMC Yukon brake lights work by receiving power from the brake light relay switch. The brake light relay switch is connected to the brake pedal.
Check for power at brake light switch Check for power and ground at the brake light sockets open wire?
There's continuous power supplied to the circuit. When the switch contacts, it closes the circuit and allows the power to go to the brake lights.
Stuck brake light switch, or a short to power somewhere in the brake light circuit.
If you have the same bulb for brake and signal, brake light power needs to be interrupted by the signal lights, The brake circuit has to go through the signal light switch so the problem could be there.
the brake light wiring often runs through the turn signal switch i would test power going in to the brake light switch on the pedal and power coming out when pedal is depressed if power is ok suspect turn signal or hazard switch
Check the brake light switch located on the brake pedal lever. If there is power to the switch but nothing coming out replace it. Did you check the bulbs? Is there power to the rear sockets?
Check your fuses first. If those check out, pull out the tail light assemblies. Check the bulbs. If those check out, test for power at the connectors to the tail light assemblies with a test light. If you have power to the brake light circuit (with the brake applied), then the issue is in the tail light assembly. If not, go to the brake light switch located at the top of the brake pedal. Test for power at the input... there should be constant power to it. If not, there's an issue with the power supply, and you'll have to trace it to the fault. If so, test for power at the switch output with the brake pedal depressed.. if there's no power there, the switch is faulty. If there is power there, then you'll have to trace the wiring towards the tail lights to find the fault.
You may have a bad brake light switch that is located behind the brake pedal. It is also possible that a wire is off on the switch. Check for power on the positive side of the switch and see if you have power to the other side of the switch when you touch the button. If you do, then you have a broken power lead to the brake lights or a broken ground in the trunk