MG MGB to November 1967: Roadster to GHN3-138360, GT to GHD3-137795
Triumph TR4 and TR4A (1961-67)
Land Rover Series II and early Series IIA (1958 to April 1967)
The voltage stabilizer is pretty unique to British cars of the mid sixties through mid 1970’s. As a component it was added in as the suppliers of electric gauges changed their specifications. It’s also referred to as a ‘voltage regulator’, which is more correct. Instead of the instruments running on 12 volts, they ran on 10.5 volts. This gave them better response, especially variable resistance gauges.
The voltage stabilizer essentially changes the line voltage from around 14.5 to 10.5. If it fails the electrical gauges (except ammeter/voltmeter) will either read too high, too low, or not at all.
This is important to know when adding or replacing gauges. New instruments that require the stabilizer are still available, and if adding a new one make sure to pull the power for it from the stabilizer and not any old hot lead from the vehicle.