Bombi headlight troubleshooting

We've got a mid 80's Bombi that we have no headlights or dash lights on.

So far have checked all known fuses, all known ground connections, and all accessible areas of wiring harness to verify nothing out of the ordinary.
Have also replaced voltage regulator, and of course have verified both headlights do work under direct power. Have also verified that we do not have voltage out of headlight wiring, and that all dash bulbs are functional, but will not light.

Short of isolating sections of wire and verifying continuity wire by wire, is there a smart way to troubleshoot this issue? Any relays or other likely problem areas that we should check first?

All other exterior lighting, and interior dome lights, etc., do work fine.

Any ideas are appreciated!

I would use a test light to check fuses ground the alligator clip and touch both sides of the fuse holder. if the circuit tester on both sides you have a good fuse and good contacts next I would go to the headlight switch check to see that the switch has power and is passing power when you switch it to the on position I believe the bombii has high and low beams you will have to locate that switch should be a stomp switch like an old car from the 70's down on the floor if it has one of those your problem will most likely be with wires or contacts corroded away as for panel lights it could be related or a different problem with the dimmer circuit if it is related my guess you have a problem with the power source to the headlight switch. most cats I have seen get power from the back of the ignition switch you may have a broken wire there or a bad connecter.

We did check continuity of each fuse through the fuse box. The headlights are actually actuated by the ignition key (key on = headlights on), and the dimmer is on the ram steer post. we did not check for power immediately out of the terminal on the back of the ignition. I think that will be next on the list. Anybody ever heard of a good wiring schematic for these Bombis?
I gathered the one in the manual was pretty basic and useless, although I did not see it personally. Thanks!