What does the wiring for headlights look like?

A single wire goes from the headlight power switch to the high/low beam switch. Two wires, one for high beam and one for low beam, go from the dimmer switch to the front of the car, and a typical headlight circuit contains color-coded wires.

A dark red wire is the battery circuit hot wire, and the ground wire is black. The on/off switch wire is yellow. The low-beam power wire is green, and the high-beam power wire is bright red. When using relays, a dark blue wire goes from the low-beam power-out switch to the low-beam relay. A purple wire goes from the high beam power-out switch to the high-beam relay.