It should turn on your underdash lights and you should have the wiring already under the passenger side speaker for a soundbar with light.

 

Don't know about the YJ but my late model CJs have the light/dimmer switch combined. Full counterclockwise turn is a click that turns on the dome light in the back of the hard top above the liftgate, and turns on the underdash lights. There's a wiring connector on the driver's side rear corner interior to engage / disengage for hardtop installation / removal.

 

I should have shared this a long time ago. Nearly all CJ's are wired for underdash lights. My 83 didn't have any, but I found some in the junkyard and they plugged right in. The lights are under the dash on each end. They have little white plastic dome covers on them. A lot of the old wagonners and FSJ's have them to. Unscrew them from the dash and unplug the wiring. A black wire goes to a bullet connector coming out of the headlight switch connector. A orange(I think) goes to the fuse box. Look at your headlight switch plastic wiring connector. It probably has a short black pigtail with a female bullet connector hanging off it. use a test light hooked to 12 volts and probe this connector. Turn your switch on, the light should come on. The switch connects to ground. The orange wire at the fuse box is hot all the time. You can look in a haynes manual for the wiring diagrams also. Mine is for a cherokee but they are probably the same. It has a diagram of the headlight switch and marks the connector for the dome light with a "D". This terminal is grounded when the dome light switch is on. Leave me a message if you have any questions.
Greg

Greg
89 XJ, 83 CJ-7, 79 Blazer, 67 CJ-5

 

Here goes - I have a 94 YJ AND the factory service manual. AND I fixed up my own overhead light assembly. AND I can add two and two and get four. (I think!)
The first thing is to know that the over head light circuit in almost any car made since WWII (dubyuh-dubyuh duece) in always HOT. The on and offf is by making or breaking the ground circuit! I got an overhead light fixture from a salvage yard that had a "spot light" to the left and same to the right and a normal light to the middle for area lighting (I think it was a Ford PU) and mounted it in the 'sound bar' furnished by the factory (in early '94 the 'sound bars' did not have a light and in later '94 they did and they cost $270 if you had an early one and wanted lights)(easy using common sense since the sound bar consists of a lot of foam and fabric)(it doesn't need to be 'heavy duty') and wired it thus: go into the factory wiring harness (you'll need a factory service manual for this if you decide to do this) and interrupt the ground circuit to the interior lights. This will give you the ability to turn off the interior lights at will to keep the battery from running down or simply for some "stealth" technology as you see fit or need. (I need!) The next thing is to get a hot wire to the new over head light fixture (no matter what model) and that comes from the same source as the factory (the battery, what else?) through various connections and etc., etc.)(and I will e-mail you with this if you want it) and fix it so that the light comes on from the battery direct or from a switched connection so that it only operated from the switch (ignition) or direct. The latter is super convenient and the former is safe. Mine is super convenient. Let me know. I will be glad to help. That is what this BBS is all about.
sln