7 volts would not be an overcharge situation on a 6V system. I drove my truck about 50 miles yesterday and I had swapped the ammeter wires because the previous drive showed discharge at highway speeds and charge when first turning the key on. The ammeter now shows charge, about 1/2 way to full charge at speed, although I have not measured charging voltage.
My new battery (1 day old) was dead halfway thru the drive after a stop (brake return spring doesn't shut off the brake lights), but I think I may need to look at the voltage regulator, which might not be disconnecting the battery when stopped.
