1990 Chevy Truck headlights

Usually the circuit for the headlamp isn't fused, part of the headlamp switch is a circuit breaker for the headlights, the feed for that circuit probably comes from a fusible link, battery junction block. The red wire at the headlamp switch should be the feed to the switch for the headlites.

The taillights--dashlites, whatever, is usually a fused circuit.