Brake lights and turn signal switch

Had the same problem recently. Make sure all of the connections at the turn signal switch are tight and well insulated from one another. Also make sure that any paint or crud on the bulb housings is completely cleaned off.The housings ground to the metal of the body so you have to have good bare metal to metal contact. Finally(and this is the one that nearly killed me!) I had put in new bulb housings and both wires were black,I had the wires reversed! I kicked myself for days on that one! Good luck!