Also check that capacitor on the bottom. disconnect it and see if fuses blow. It shouldn't pass any voltage to turn a test light on. You do have a test light right? That is a filter capacitor that smooths out the voltage going into the regulstor.
To check guages, use the regulstor output, (5volts pulsing?) with a 10 ohm resistor in series with the ground side of the tested guage. the needle should go to "F" or "H" and not go higher or lower.
The regulator is simple. The case gets grounded, the terminal in gets 12v, and the output goes to the guages. I use a small 12v battery from my hand held spotlight, to power stuff up for bench testing and a couple of alligator clip ended test wires.