914 volt meter question

[Menmojo]

I’m working on a 1975 914. I just replaced a non working volt meter with a working period correct vdo volt meter. When the car is shut off the volt meter is reading the voltage.
Is this correct? Is the volt meter supposed to be switched on with the ignition or does it always show the voltage? I’m concerned that it will slowly drain the battery. The car has the stock wiring harness and originally came with a center gauge package.

[Dave at Pelican Parts]

It should be switched with the ignition. The clock power is unswitched, I believe, so you may have gotten those wires changed around.

--DD

[Menmojo]

Thanks. I did have them mixed up.
Now the volt meter works however I have another issue.
When I turn the headlights on the volt meter in the car drops to zero.
I tested the voltage at the battery and it reads approximately 13.7 so I assume the charging system is correctly working.
Do you have any idea why the voltage gauge drops to zero when the headlights are turned on?

[phelix]

Do you have the 12v supply for the illumination of the gauge plugged into the ground on the gauge? Double check the wiring at the gauge.

[dr914]

if it drops to zero you probably have a grounding problem

[phelix]

That's my thought - that it might be grounded through the bulb which works when the lights are off but not when they're on.