'85 D100 P/U 318 - auto NO CRANK ? / No Headlamps ?

My good friend has '85 D100 Pickup 318 / auto that has fully charged battery and power to starter yet has NO CRANK + NO HEADLAMPS ? He's looked at fuse links and all look good . Any ideas ? This one has us stumped big time .... All help warmly appreciated & acknowledged

I'd start by pulling (seperate) the main power in bulkhead half & check for power/continuity to the other half. grab your meter and some jumpers

Then check the amp gauge wires.

THANK YOU ! He's checking this afternoon .....

Fuseable link or main power source connection at the bulkhead