'69 Cuda temp gauge not working

Last summer when I first drove my Cuda after a pretty extensive restoration, one day my gauges seemed to be acting funny. I discovered that the temp sender wire and the alternator wire got too hot and melted their insulation together right where they lay on top of the passengers side valve cover. This is on a big block engine. I presumed that the reason this happened, is because I used a valley pan gasket with the ports blocked to reduce the heat to the intake manifold. This 'new' hotspot is exactly where it proved too much for the insulation.

So I replaced the melted sender wire, and enclosed the wires in a heat resistant sleeve where they cross over the engine. I also replaced the temp sender with a new unit.

Predictably, my temp gauge doesn't work any more, even with the new sender. The fuel and oil gauges still work, so I assume I probably fried my temp gauge? Is there an easy way to bench test the gauge? I plan to dig into this again this weekend, and just wanted to get some opinions from the experts.

This is on a '69 Cuda with the rallye gauges. Thanks in advance for any help.