Dash lights not working

This is the ivr I got wich is the one on the dash 1966-1974 Instrument Voltage Regulator For Dodge Challenger Charger Dart Cuda Satellite | Custom in the description is said is was for 72 scamps and newer but I thought it would be ok since it the same dash and stuff but I don’t know if that really matters and then I just ordered a new headlight switch as well. Another problem I was having was when I plugged in the dash out of the mounting place to test is the gas gauge started to work but when I put in the dash and plugged it in the gauge stopped working but it has never worked as long as I’ve owned the car