electrical problems

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.

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

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