1967 Mustang - Break lights not working

[Paul 69 Mach I]

Trish, My rule of thumb with fuel problems and electrical problems is REPLACE IT! Ford never intended your 67 to still be on the road 38 years later. The parts were not made & never intended to last that long. I've watched a friends Camero turn into a burning ember on the side of the road after he "fixed" a electrical problem the easy way. I was also at a cruise night when a Nova who's owner "fixed" a fuel problem turn into a crispy critter.
My son decided he wanted a classic. It needed a new motor. We took the motor out & replaced all the wiring bumper to bumper. Yes, wiring is expensive. But after putting in new wiring several problems magically corrected themselves. In the long run it saved money.
Don't be afraid to replace the dash harness yourself. Pull the dashboasd & route the new harness alongside the old one. Start from the far side & unhook one plug at a time into the new harness. That way when your back as mounting the fuse box everything should be fine. Good luck and enjoy driving it.