1966 / How can I check the small voltage regulator mounted on the back of the gauge cluster.thx.

 

Use a digital or analog voltmeter. Set it to read 20 volts. Turn the key on.
Put the red lead on the terminal of the regulator with the black-green single wire.
Put the black lead on a good ground on the dash, not the gauge cluster. It should read 12 volts or so. If you don't have 12 volts, the problem is before the regulator.
Now put the red lead on the other terminal(with 2 wires), it should read 5 volts. An analog meter needle might be bouncing a bit, but average around 5 volts. If it is over 5 volts the regulator is bad.
If the voltage reads 0 then disconnect the terminal. If the voltage goes up then a gauge is shorted.

 

I replaced mine three times at $24.95 each until I came across a new electronic one (no moving parts) for $49.95. The electronic one finally works. Of course the old mechanical one worked for 40 years until I replaced the bezel.

 

The electronic ones are an unbelievable ripoff.
You can get a 7805 - 5 volt regulator at Radio Shack for around $1.50.
I buy them in quantity for 25 cents. I have a home made electronic regulator in my car. It even survived a dead short when the gauge slipped and shorted aginst the metal support.

If you are interested I will come up with some photos on how to do it.

 

I'd like to see how to make one. My Brother in Law said he knew there was a way to make one from Radiom Shack parts but we couldn't find anything on it. After pulling my dash apart 3 times the $49.95 was well spent but in case it craps out again I'd rather spend $1.25 to fix it.