1994 GMC Truck electrical problems

Did you use a voltage tester on applicable fuses and links? Even if the fuse is good, if no voltage, the circuit is dead. Check the feed to and from the head lamp switch. In the diagram, voltage feed comes in at the top. The right side feed for switch is usually for the dash lites-- tail lites and such, should be fuse protected. Voltage feed to the left side of switch should be head lamp only, circuit breaker internal to switch. The feed to the left usually comes from fusible link. the brown wire from headlamp switch should be voltage for tail lamp.