1990 Buick Century no dash or running lights

I'd have to check circuits going to and from, headlamp switch. Your headlamps circuit voltage is not controled by a fuse, there is a circuit breaker in the headlamp switch, only for the headlamp, that part of circuit gets feed from fisible link. Your other circuits, dash lites-- taillites are a fused circuit, does go through the headlamp switch. Use a voltage tester on the instrument lamp fuse circuit, if you haven't already, even if the fuse is good, if no voltage on the circuit, the circuit is dead.