1970 Dart Headlight Switch

You need power out of the other end of that fuse. I've seen glass bar fuses broken underneath the metal end cap and crusty contact clips in the fuse box too. There are other lamps on this orange wire circuit. Checking power through the dimmer to orange wires is easier checked at those locations. Do radio, ash tray, shift indicator lamps work?
I don't argue that the dimmer is a common culprit turning off all these lamps. May as well fully diagnose.