Classic/Antique Car Repair: 1970 Mustang, electrical tester, mustang

Question
My 1970 mustang stop light on the left side doesn't work but the right side does, also both of my turn single works fine. How can I get the left stop light to work?

Answer
First, check and make sure the bulb is not in the socket backwards. Even though it is a one way only fit, it can be forced in backwards. Once that is checked, and the bulb is tested (can simple move to right side to check) if it still does not work, it has to be the wire from the brake signal. Use an electrical tester or even test light to trace back the wire and find where the gap is, The wire should conjoin with the right side, so you should not have to trace too far.