There's a couple of possibilities for interior lights staying on that are both related to that switch.
One is that the switch is actually designed to turn the interior lights on. If you have the dimmer turned all the way up, i.e., one stop past maximum brightness, the interior lights come on by design. So if it's accidentally been rotated all the way up, the lights will stay on.
The other possibility, especially if they come on randomly or flicker on and off, is that the switch is bad. People often complain of flickering dashboard lights as well as the dome lights when this happens. It's a very common issue on the early KJs. As has been mentioned, simply turning the dimmer down a notch or two can sometimes make the problem go away. But it's a temporary fix. Gradually as the switch becomes more and more worn, that doesn't work anymore (guess how I know?). Eventually even your headlights can become involved and randomly switch on and off at night (again, guess how I know?)
If you want to permanently fix it, you have to replace the dimmer (or rheostat) switch, along with headlight stalk and the turn signal stalk on the other side together. They are all one part, called the Multifunction Switch. If you're even slightly mechanically inclined, you can replace it yourself in less than five minutes. All you need is a torx screwdriver to remove the two screws under the plastic shroud around the steering column. Dealers charge more than $100 for the part, but if you shop around online (Google "wholesale mopar parts") you can find it for less. Just be sure you get the right part for your model year: there's one with fog light controls and one without.
If anyone wants detailed instructions on how to replace the switch, just PM me.
Last edited by soulfinger; 10-01-2009 at 03:37 PM.