Start by checking the ground wire for the right socket. If no problem is found, use an inexpensive digital voltmeter to measure the voltage on the side of the brass base of the bulb while just the running lights are on, and again with a helper when just the brakes are applied. Holler back with those numbers.

Answered by caradiodoc (expert)
17,277 answers provided

it might need a new socket,sometimes they rot away.

Answered by dave's big backyard! (expert)
264 answers provided

check the voltage at the turn signal switch.it controls both of these.i agree with car about the possable bad ground.

Answered by cadieman (expert)
2,854 answers provided