big volts

If your meter is going from 1vto 16/18 when on the DC mode, switch it to A/C mode. I bet one or more diodes are bad and its sending A/C out, through the system. The VR wont know what to do with that. Neither will the battery, or anything else except light bulbs. Bulbs run just fine on A/C. That may be why your headlamp sw quit. That would also explain the high and low voltage readings on the two ends of the same circuit.
Check it out.