how to bench test a 70 Dart instrument cluster?

I have been completely rebuilding a 1970 Dart including all new electrical.

Of course the one thing that didn't work in the whole electrical system is the thing that is most difficult to get to - the instrument cluster. Everything on the right side works fine, the dash lights work fine all across. What doesn't work are the 2 gauges on the left - gas and temp. These are the two gauges that go through a voltage limiter. The gauges, circuit board and the voltage limiter (modern version from RTE) are all new. There is 12 volts at the wire that supplies the voltage limiter and then the gauges. You can hardly get to anything from under the dash. I pulled the cluster out again today to figure it out.

As far as I can tell all it could be is the voltage limiter, the circuit board or the gauges. Gauges are buried to the left with gas in the tank and the engine up to temp (using a heat sensor gun). I'm hoping someone can help with some advice on how to bench test this stuff: what do you use as a power supply? RTE gave me instructions for testing the voltage limiter out of the cluster using an led that is part of the limiter. I can't figure out how to test the gauges on a bench, especially since power has to go through the limiter which evidently pulses to replicate the points in the original.

Any suggestions would be appreciated