I have a 2000 gmc 1500. The brake lights keep going out and the left turn signaldoes not work. I replaced the bulbs but they still don't work.

scroll down this page until you see a question just like yours ..there are a few perfect answers there, tenspeed and dandyoun seemed to know

Turn signal switch is notorious for preventing brake lights from working since they are run through the switch. The only light that will come on in that case is the middle light above the glass.

will add that the circuit boards where brake light and tailight and revere light bulb go bad, check and see if you have voltage a connector at circuit boards at the back of the tailamps, can purchase new circuit boards at local parts store