Check the Relay: Sometimes a faulty relay can cause headlights to stay on. Locate the headlight relay in the fuse box and try swapping it with a similar relay to see if that resolves the issue.
Inspect Wiring: Look for any frayed or damaged wires that could be shorting out. Pay special attention to areas where the wiring harness might rub against metal or where it could be exposed to moisture.
Ground Connections: Make sure all ground connections associated with your lighting system are secure and free of corrosion. A poor ground can cause all sorts of electrical issues.
Headlight Switch: Even if the switch is new, it could be defective. Sometimes aftermarket parts can have issues. If possible, try testing with another switch or go back to the original to see if that changes anything.
Fuses: Double-check the fuses related to the headlights and signals. A blown fuse can sometimes cause erratic behavior.
Check The FSM Wiring Diagrams: You can find a
free copy of the FSM with all the wiring diagrams here.