To check the dash lites, pull off the 3 terminal connector on the dimmer switch. 2 terminals (orange wires) go to the rheostadt for dimming the dash lites, the other terminal is for grounding turning ON the dome lite.
Next turn ON the headlite switch, take a voltohm meter and measure one of the orange wires you should have 12V in one of these. Turn the headlite switch ON/OFF the 12V should go OFF. If the above worked, insert a jumper lead between the 2 orange wires now you will send 12V to the dash lites and they should be working when the headlite switch is ON. The rheostadt is simply a variable
series resistor to drop the 12V for dimming the dash lites.
Hope that helps..
Just my $0.02..