02 sportster 1200 brake light not working

Check for power and if none trace back to fuse

there is a break pressure switch on the brake line with 2 wires plugged into it -- replace the switch and your brake light will work

I would suggest a circuit for the brake lights has shorted out somewhere causing the brake lights to have power constantly!

you will need to trace the wiring from the brake switch to the brake lights and check for shorting out.

Wiring is hard to diagnose without the bike.

Short to main accesories which is dash lights headlamp and tail Lamp not the break lamp it's prolly on the ground wire side since some lights still work ther getting juice but the ground that compleats the circuit to the break lights gets there through the break switch ok but the ground from the key on switch isn't getting to the constant on light start at the try to run new grounds to anyplace and if the lights com on its in the harness and u start tracing it down when the bike is striped of tank and sheetmetel it will be Easter to find look at the harness connectors for green oxidation and loos fitting wires

trace all your wires theres a break somewhere

Sounds like you had a short circuit in your tail light/ brake light. When you depress the brake pedal, the short circuit loaded down your electrical system.

Orange/white = 12 VDC
Blue = 12 VDC for tail light
Red/yellow = Power from brake light switch (to stop light)
Black = Ground(s)
Purple = Left Turn Signal
Brown = Right Turn Signal

Yes, you need to of course check the voltage coming into and going out of the brake light switch, if 12 Volts are there going out and coming in while pressing on the brake pedal, your brake lights aren't getting a good ground or there is a break in the circuit between that switch & the lights.

On occasion the tail lights will work with a weak ground circuit where the Brake lights won't. Best way to determine this is to just hook up the 12 volt tester to the Brake light hot wire & there at the bulb ground, then in an area away from the bulb that has a good possibility of contact/ground.

Really that's it, if the 12Volts is getting to the bulb but it isn't lighting, if you aren't getting the voltage there and the brake switch is hot on both sides when pressed, the break in voltage will have to be traced from that switch to the tail light to find the problem.

good luck.

Replace the bulb in the tail light. It's dual filament bulb. Brake light is separate from the running light.