Brake lights inop on my 88 T-bird

You have no clue, guessing won't fix it , having wiring diagrams an using a DVOM - digital volt ohmmeter will. Testing an reading how they are suppose to work will. factory service info.

Turn Lamps
Battery positive voltage (B+) is supplied at all times to the turn signal/hazard flasher module in the hazard switch assembly from the rear fuse block T/SIG HAZ Fuse. The turn signal/hazard flasher module is permanently grounded. Battery positive voltage (B+) is supplied with the ignition switch in the ON or START position to the turn signal switch in the instrument panel from the rear fuse block IGN 1 Fuse.
When the turn signal switch is placed in the position to indicate a LH turn battery positive voltage (B+) is input to the turn signal/hazard flasher module Left Turn Input. In response to this input the turn signal/hazard flasher module supplies battery positive voltage (B+) in an on and off flashing pattern to the LH turn lamps and the instrument panel cluster (IPC) LH Turn Input. The LH turn lamps are permanently grounded so the LH turn lamps light when they have power, ground and turn off while power is removed. The IPC will also light the LH turn indicator.
When the turn signal switch is placed in the position to indicate a RH turn battery positive voltage (B+) is input to the turn signal/hazard flasher module Right Turn Input. In response to this input the turn signal/hazard flasher module supplies battery positive voltage (B+) in an on and off flashing pattern to the RH turn lamps and the IPC RH Turn Input. The RH turn lamps are permanently grounded so the RH turn lamps light when they have power and ground and turn off while power is removed. The IPC will also light the RH turn indicator.

Did the turn lamps operate properly?
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Go to Step 3
Go to Turn Signal Lamps and Indicators Inoperative - One Side
3
Disconnect the instrument panel cluster (IPC) connector.
Connect a test lamp between the inoperative turn signal input circuit at the IPC connector and a good ground.
Turn ON the ignition, with the engine OFF.
Move the turn signal switch to the inoperative turn position.
Does the test lamp turn ON and OFF with the turn signal lamps?


You people need to quit trying to play auto mechanic , you have no clue about automotive electrical circuits .

Have you checked the bulbs already?
Don't know what kind of car you are dealing with here.
Most vehicles - the brake lights and rear turn signals share the same electrical circuit to the rear tailights. Usually the turn signal switch will separate which signal goes to the back.
Do your brake lights work? Is there a High mounted stop lamp and does it work?
I have seen a Hazard Switch be ON and fuse blown causing the Hazard Flasher to be inop - which prevented the turn signals from working. Turning OFF the hazard flasher brought back the T/S.
Check the rest of the lights - see what does and doesn't work - and do the front turn signals flash? Stay On? Or flash really slow?
Let me know what you find out and if this helps you at all.

Sounds like your multifunction control switch needs replaced. Its location is on your steering colum.

YOU MIGHT HAVE A BURNT OUT RELAY IN FUSE COMPART UNDER YOU CARS HOOD CHECK THAT OUT THRU YOUR CARS MANUAL,IT WILL SHOW YOU WHICH RELAY IT IS?

CHECK YOUR RELAYS,FUSES

brake light dont have relay only fuse brakes are hot at all times on gms. in goes from fuse to brake pedal switch to hazard turn signal switch then to brake lights. ck fuse if good go to pedal switch if good go to turn /hazard switch the turn signal hazard brake all use same wire to lamps.

The turn signals and the brake lights go through the hazard switch. Try cycling it a few times and see if that solves the problem. If the fuses are good and the 4way's don't work, I would suspect that switch.

IF THE TURN SIGNALS STILL WORK IN THE FRONT, THAT MEANS THE FUSE & THE FLASHER ARE OK. IF THE SIGNALS DON'T WORK AT ALL CHECK TURN SIGNAL FUSE & STOP / BRAKE FUSE. ARE YOU SURE THE CORRECT BULBS ARE BEING USED?

Replace the multi-function switch located in the steering column.

Your brake light circuit runs thru your turnsignal switch if your hazard switch is on your column I have seen numerous inop brake lights caused by faulty turn signal switches.