Both fuel gauges flick immediately to full when I turn on the ignition.
The volts at the changeover switch are around 6v, so I wonder if my volt stabiliser is at fault.
I'm keen to know a fix, coz it's a pain lifting the seat and peering in the tank to check if I can make a journey or not!
If you have a '65 motor then there isn't an instrument voltage regulator as far as I'm aware, the instant reading gauges (with the little arrows on the end of the needles) didn't have one. This came in from '67 onwards (suffix D black dash neg earth) with the slow reading gauges when the water temp gauge became standard, replacing the ammeter. The only exception to this is military clusters (the type with both oil and water temp) as these are either capillary or electrical designed to work with full voltage.