Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: headlights not working
A bad dimmer switch can cause the lights to not work at all, but it's unusual. More commonly one side of the switch goes out, usually low beam. A headlight relay was not a factory part on older CJ7s, and I doubt one was used on the late ones but I don't know for sure.
Before you throw more parts at it, take a systematic approach. There are three wires going to the dimmer switch. The red one with the white stripe carries power to it. The gray and gray with white stripe are the low and high wires to the bulbs.
Unplug the connector from the dimmer switch, turn on the headlights and see if you have battery voltage on the red wire. Then test the resistance to ground on the gray wires. It should be a fraction of an ohm.
If that tests out, it is almost certain that the dimmer switch is bad. If you don't have power, the problem lies in the headlight switch or the wiring from it to the dimmer. If you have an open or very high resistance on the gray wires the problem is in the firewall connector or the wires from the dimmer to the lights, or from the lights to ground. Don't forget to checkj your grounds.