E.L. dash lights on the 66-67 Charger use the same basics as the 60-62 Chrysler 300s. The power unit is the same for both cars, and can be rebuilt by any competent electronics person. There is no connection between headlight motor function and the dash lights, unless the headlight switch itself is bad. If any--repeat--any-- gauge or radio light malfunctions in a 66-67 Charger, it will shut the whole dash light system down. The console shift illumination strip is included in the system...that's the one that many overlook. One way to test for a bad light circuit is to remove the entire dash cluster, rig a 12v source running through a spare power pack(known to be good, and don't forget the ground wire)to the cluster and bypass each gauge until you find the one that's bad. Keep in mind the radio dial is E.L. also; one other thing, check to make sure the rheostat dimming function is good on your headlight switch.
Use caution, the power pack changes DC current to 200v AC to make the gauges glow, so it will bite. Ask me how I know.