Brake lights will not work turn signal works fuse is ok

Hazard switch might be on

Do turn signals work ok? Do you have current at the brake switch?

check relay in fuse block under hood

Since the turns work in the back, that means the brake bulbs are good. Brake lights and turn signal lights share the same filament in the bulb.
There is a fuse for the brake lights. Then, there is a brake light switch on the brake pedal. You need a voltmeter or test light, after checking that fuse is good. Need to check if fuse has power on it. This is one of those fuses that are hot at all times-as long as battery is connected, voltage should be going through the fuse and up to the brake light switch. Check for power both places. The switch on the pedal is a simple on-off switch. When brake is depressed, the spring loaded switch is turned on-passing power on towards the brake lights.
But then the brake wire goes into the turn signal switch before going on to the brake bulbs...however, since your turns work good, I doubt if there is a problem in the turn switch. First check if the brake light switch is sending power on when switch is on.
Let me know what you find. Good luck.

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?

If the third brake light works and the regular ones don't, it is most likely a bad turn signal (multifunction) switch. The switch is able to kill the brakes lights to run the turn signals, and in rare circumstances does this. I've seen it several times. It could also be wiring, especially near the turn signal switch, but it is usually the switch.

faulty turn signal switch would effect brake lights if its faulty.because brake lights and turn signal feeding off same circuit.

there is most likely a short in the wires have you put a tow package on it if so did you splice in to the lines check all wires and see if they are burnt any were most likely short

relay