[Peter Serio]

The factory ground for 64 and 65 Pontiac A body cars was a single black wire. At one end (white arrow) that wire is attached (uncovered) to a flat plug-in tab which was made onto the side as part of the silver-metal bulb socket with the lime green wire in it. (That lime green wire gets 12 volts of + battery power when you turn your high-beam headlamps on.)

The black wire then goes into the tape wrapping only to re-appear underneath the dash above the brake pedal support. The other end of that black wire is a crimped "ring terminal" end. The ring is secured to the side of the unpainted support structure which is part of the under-dash reinforcement for the pedal(s) and the master cylinder. There was a small star washer in-between the ring end and the brake pedal support.