I too, would like a voltmeter for my '50, but I do not want to do any dash crawling to do it.
I ordered a unit which plugs into the cigarette lighter socket. It looks like a plug for cell phone charging wires with a digital display for volts.
I haven't received it yet. I'll let you know if its worth a dern.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission