Lights doesn't work
If it's not the bulbs, possible causes are bad headlight relay, fuse, module, headlight switch, dimmer switch or wiring. You need to track down the problem.
In 1977 there are fuselinks right by the starter solenoid on the passenger inner fender right where the positive battery cable is connected, check those first, if those check good then move onto the dimmer switch, these have been known to stick between modes even thought it may click it may not be working, then the headlight switch, usually these will cycle the headlights on and off just before they go bad but sometimes they just quit.
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