512 BB dash lights

all dashlights?
if so look first at the knob where you can turn to make the lights darker

 

Rheostat on the dash is the problem. When you rotate the dial there should be some drag, less drag rotated to the left.
You can take it out of the circuit and not worry about the dimming feature.

 

use a voltmeter or a testlight and check if there is power at the dimmer/rheostat