I restored a 72 xr7 a few years back and was having what appeared to be demons in the rear taillights….restored housing…sockets and reworked wiring that had been bench tested…along with a new Ts switch. After much dismay and inappropriate use of the English language…it turned out to be a tang on one of the terminals that I had evidently removed before fully released from the turn signal switch plug and had jammed in the plug is a way to connect two adjacent wires….I remember how happy I was to discover it…how long I had looked for the culprit and how I was unable to blame it on anybody else but me.