I have changed my third brake light completely and it still doesn't work. what else could be wrong with itq

does ur third brake light work??if not i would see if maybe u had a broken wire at ur brakelite switch. very possible with all the constant moving of pedal..also plz make sure bulbs are good. i have seen both side blown .hope this helps

Check the voltage or the connection.
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Multi-Cardiag M8 CDP for car and truck

Check for loose contacts or wiring that is causing a short circuit near the brake pedal, or at the rear light.

could be the switch under your foot pedal. They gunk up over time.

Check the groundwire to the lights.

take a test light and make certain your getting power to the socket. could be a bad socket

Have you checked the brake light switch by the brake pedal?

I had that same problem with my Dodge Durango, my back brakes ran on the same fuse which means all my brake lights woulda been out, so I changed the bulb and it worked fine after. However I had to lift my truck to change my third light, u might have to change from the truck or take off from back window

Try checking all of your rear brake lights to see if they are working.If you have a burned out bulb the control cannot complete the circuit and the cruise will not work. Dont forget the third brake light sometimes have more than one bulb in them so check closely to make sure that all bulbs are good.