Fuel guage vibrator voltage

[Mrpatjr]

72 vw standard sedan. How many volts should the reading be on a fuel guage vibrator before it goes thru guage. Mine has an additional reducer as we'll. is that what someone put on or is it factory. Burned two gauges already.must be the 12 volts is causing the burn out replaced sending unit already and fuel guage foes work when tested w 9 volt battery w/o vibrator.

[Marc]

The vibrator output is square-wave AC, so it's not possible to measure a constant DC voltage level. What's important is that there be a reliable discharge path to ground - if not, the output voltage will rise to supply level which will smoke the guage. If the speedo housing doesn't have a good ground, or even if the little screw which secures the vibrator to it comes loose, say goodbye to the guage.
There are two basic types of regulator, the original bi-metal "buzzer" version and the more modern that has a zener diode and a lightbulb inside. Possibly at one time yours failed and someone added another without removing the original, or you could be looking at a radio-noise-suppression filter. Got a picture?

http://www.speedyjim.net/htm/fuel_ga.htm

(Disregard the "balance-coil" section, Beetles all use the "thermal" type guage & sender)

[Mrpatjr]

Here is pic of what I have

[Marc]

I believe that black part is some sort of "choke" (coil) for radio noise suppression. I've never bothered to unwrap one to verify that, but they're often present and should have no effect on voltage regulation - you can verify that for yourself, the voltage should be the same at either end of it when power is applied and the vibrator is grounded.