[mike9292]

I have a 1967 mustang, and right now im having an issue to where the brake light wont work when the running lights (headlight on) are on, but does work partially when the running lights are off and the blinker does work. By the way it is happening on the drivers side, not the passenger side. Any and all help will be appreciated.

 

[mike9292]

Also, when i press the brake the taillight goes out.

 

[Route66UK]

Sounds like a bad earth to me.
could be a simple cheap fix, check that first on the driver's side..
all the best.

 

[mike9292]

Turns out it was the ground, thanks for any help anybody.