Gauges in my 70 shorting out

Try and replace the instrument voltage regulator. You can get reproduction ones or you can make your own solid state one. There are instructions laying around the forums and internet.

I had the opposite problem, My guages would read normally then at times peg the high side. Found out that the amp meter connections were not seated correctly on the circuit board and current was leaking from the amp meter through the connection to the other guages bypassing their sending units thus making them peg full scale.

Your instrument volatge regulator connections can do the same as they are sort of similar to each other.

Since all 3 guages ground through their sending unit, and all 3 seem to not work at the same time, my guess is the instrument voltage regulator.

its on the back of the instrument panel. pull the whole cluster out and youll see it.

looks like this

I also vote for buying or making an electronic one. We made one similar to this one.

http://chris66dad.tripod.com/id29.html