1975 Chevrolet Cheyenne lights

check brake light switch then check to see turn signal switch is sending through to bulbs or not check dk grn and yellow wires coming from t/s switch..

ok, changed out switch. still nothing

then check toseeif power is going into switch don't start replacing uneeded parts. it may be a short. there are three wires going to back lights, brown for taillights, and yellow and drk green for stop/turn sigs. see if brake light switch is sending power to t/s then it may be a shorted wire or a bad ground which for tail lights is usually at very back of frame on lh side. also check flasher if that is bad t/s won't work. there is a flasher for hazard and another for t/s. get a test light or volt meter to check.