Courtesy dome light
I don't know if this will help or not but I'll through my two cents and we will see. The only experience that I have is with the factory set ups. Most courtesy/dome lights are wired hot. A wire that is always hot (whether the switch is on or not) is ran from the fuse panel to the light and then the ground wire is ran from the light to the switch in the door. All of the basic factory dome lights that I have worked on are wired this way. The switch actually completes the circuit. If you are going to work it with the head light switch then you will need to tee off the ground wire and attach it to the ground leg that is on the head light switch. You can find this leg with an ohm meter. Simply turn it to the position that turns the dome light on and check around on the terminals for circuit to ground. Once you find it check it a few times to be sure. When you find it you can also verify that you have the right one by turning the dome light on and unplugging the wire to the head light switch a few times.
Now this is a little deeper. You can also do all of this with a relay. You run your power to the relay and then from the relay to the light. Your ground lead from the relay is ran to the door switch and the head light switch. When the door is opened and the switch is activated it grounds the relay, the relay closes its contacts, the circuit is complete and this turns on the light. If you do it this way just run the switched on power from the relay to the light and ground the light right where it mounts. This could be useful if you wanted something else to turn the light on. Like maybe a remote or something. Using relays is cool because once you have a relay in the circuit you can figure alternate ways to turn them on. I hope this helps.
Last edited by Chris Kemp; 01-20-2009 at 11:39 PM.