ELEC--temp and fuel gauge out!! Help

1972 valiant 225.
Temperature gauge and fuel gauge out at same time. First I noticed the temp gauge fly all the way maxed out. Car not overheating. Then later that day the fuel gauge was bouncing between full and empty. Now they both sit all the way to the left. I was able to bypass the temp sending unit, attached wire from positive battery to the wire that connects to sender. No jump in needle. Checked for continuity to fire wall. Good. That's about as far as I got.
Looking at the wiring diagram for the back of the instrument cluster, I notice a voltage regulator that potentially changes the 12v to 5v? Could this be the problem? Also, how do I test all these gauges with a multimeter? Can I test for resistance or continuity? Or just volts ?
I want to get a jist of it before I take down the steering column and remove the panel. Thanks
Andy