My 77 RS ran great on a trip to Toronto yesterday charging all the way at 14+ volts. Parked it for a hour, then no start. just a loud click and volt meter goes to 0.

Checked the battery connections: OK
Tried to boost it with a car, same results: click.

Bump started it to get home, shut it off, still no start?

It charged OK all the way home 60 miles.

Relay or starter?