Everything works but the headlights.

There are several main failure areas

As mentioned, checking at the dimmer is a VERY good place to start because this sort of divided the problem into major areas of trouble.

The headlights ONLY (not park or tail) are supplied UNfused power from the "in harness splice" coming off the ammeter circuit, which is a factory welded splice, taped up in the dash harness

The headlight switch itself has a built - in breaker which can fail

The light switch CONNECTOR can become corroded, loose, overheated and fail

So if you have power at the dimmer, you can ignore all of the above

The next trouble area is the bulkhead connector, but that of course would usually just affect either hi or lo beams, not necessarily both.

Last, after the harness goes through the bulkhead, there is a separate ground wire up front which grounds the headlight connectors. Make sure it is clean and tight. I.E. you could have power at the headlight connectors, and no lights.