Help...No Power

Headlights "only" power is unfused from the ammeter circuit. Not through the fuse box. So this limits the problem area

Bad battery connection/ cable.
Bad fuse link
Poor connection in the bulkhead connector pin(s)
Poor connection at the ammeter studs on the instrument cluster

Turn headlights "on" to provide a load

Put your meter/ test lamp DIRECTLY on the top of the battery NEG post. Not the clamp. The battery POST

Stick the other lead on a bare part of the engine, carb, etc, GROUND Should NOT get a light or read any voltage. If you do....trouble in the ground cable.

If that is OK do the same at positive..........stick probe into battery POS post, and other end of light/ meter on starter relay "big" post. If you get a reading or a light, trouble in that cable.

If this is OK find where the big fuse link wire goes into the bulkhead connector. Probe that meter on engine ground, you should have voltage. "Wiggle test" the connector, try do disconnect it (there are latches) and see if you get a glimmer out of the lights

Go inside, reach up under, wiggle the wiring harness up towards the light switch. If you can get your hand up near the ammeter wiggle that, feel for heat