1966 Mustang coupe / Brake lights and left rear turn signal not working.

[ArizonaRob1966]

Replaced rear taillight harness, replaced brake light switch, replaced turn signal switch, replaced both flashers. I’m pretty sure I have the correct wire positions in the turn signals plugs. Break lights and left rear turn signal still don’t work. Any suggestions?

 

[Mach1 Driver]

This is a schematic for 66 turn signals. FYI, schematics are not wire diagrams, they simplify the circuit and show how it works:

 

[Mcmahst]

Great diagram. I would check every ground in the trunk. Remove them, use a small wire brush to clean them, reinstall and test. Lots on weird bulb not lighting is ground related. Also, you should clean the bulb sockets because they become oxidized. And if all that fails, try swapping good bulbs for the bulbs lot lighting up. Good luck.