Auto Parts: 81 Merc. capri instrumental panel, engine wiring harness, gas gauge

Question
 Hi,
I have a regulator on the back of instrument panel, my tach wont work, nor my charge indicator. Do I test it like a one way diode, or voltage coming in, for example?

               Thanks George

Answer
    Normally, the first indication of the instrument cluster voltage regulator being bad is the gas gauge reading funny.  And, it has nothing at all to do with the charge indicator.  Best way to check is to check the voltage on the instrument cluster bus (common +12V source on the printed dash)  If it's out of whack, it could be the regulator.  If your tach and charge indicator both went out at the same time, I'd suspect a problem with the bulkhead pass-thru connector or possibly the engine wiring harness where it plugs into the main harness.