I was stopped for no brake light, but the bulb was good and a new one failed to fix the problem. Trouble shooting procedures included switching sockets with no luck. Brake switch didn’t seem probable, but I don’t have diagrams to tell me how the lights are wired.
I finally found the problem when I switched the lens ass’y and found that the problem followed the lens. Further checking with an ohmmeter showed that there was an open in the bad lens.
Any idea what would have caused this problem? Everything would be sealed. I’ve seen fuses fail because they overheated because of internal resistance.
The bulb sockets can go bad. A freind’s Chevy Tahoe had a non-working stoplight. A new bulb did not fix it. I back-probed the wires, and power was getting to the bulb socket. Turns out a contact in the socket got bent out of shape. I managed to get it bend close enough back into shspe to make good contact with the bulb again and all was good.
The brake light systems in all cars are usually very simple. The problem is that an open circuit in any part of the system will not allow the brake lights to work. This includes the wires, the brake switch, the bulb sockets and the bulbs themselves. Including your make, model and year as @Tester suggests makes troubleshooting a lot easier.
If you know it is within the tail light assembly then the possibilities are limited. The Trailblazers were known for this type of problem and lo and behold, mine was struck with the issue. Removing the lens assembly, there are several fasteners holding the circuit board to the plastic housing. The circuit board has the connector and sockets. The defective solder joints were clearly visible and after touching up, have worked normally ever since.
If your car has wired sockets to each lamp, then inspect/measure the continuity from the wire through to the connector pins to find the open(s).
If they are circuit boards as described above, remove them and do the same diagnostics to find the defective connections.