Interior light stays on

My son has a 1991 limited. The dome lights and under dash lights used to be time delayed. Now they don't shut off at all. What should I check. I only found one thread on this issue and the problem was never solved.
Thanks for any help !

Check the headlight switch.
On my 89' I can turn the interior lights on by turning the headlight knob allthe way to the left.
However I noticed you said you have the delay...Check all the fuses,there should be one that says delay..pulling that should kill the dome/under dash lights..Then you can figure out where the problem is..
Haynes Manual should be helpful....maybe

If he has a problem with the rear hatch closing, that can cause the interior lights to stay on also. Learned this the hard way.

could just be a switch problem.... i would check all the jamb switches first

It turns off with the switch while your sitting in it. Then when you get out and shut the door the delay timer doesn't shut it off. This model also has the alarm system where you have to reset it if the battery runs down. It has all the bells and whistles, plus the headaches that are involved with them.

I've got a 94 with time delay interior lights...

I didnt have this problem, however the answer to my problem MAY lead you in the right direction...

As some one said above, check the tailgate lock mechanism as it may have the light switch incorperated into it...

My problem was with my after market alarm system. The tail gate would not trigger it when opened.... The sale rep/installer refused to accept it was not the tailgate switch. I knew it was not this as I pulled it out rebuilt it and tested it... FINE, nothing wring with it...

After two weeks of reading the manual and checking every thing I could, I found it was the 50cent switch in the dome light in the cargo area... BAD EARTH...

Well they all do shut off. The cargo dome. The passenger dome and the under dash lights. Then when you open the door to get out they come on and when you shut the door they don't shut off after a few seconds like they did before. Doesn't matter which door you exit either. I'm thinking if it was a switch it would not turn off at all would it ? I have an e-mail into my Jeep expert guy here in Boise.He is real partial to the XJs. He usually has the answer. just takes a little bit to get an answer.
Thanks

Sounds to me like the timer circuit device itself. I had that happen years ago (not on a Jeep) and I ended up just pulling all the bulbs out. In my case the defective device was integated into the dash so it would have cost an absurd amount to fix.

That is kind of what I ws thinking. Hopefully it'll be like the wiper delay switch and a littler box some where. That is what I need to know is where that would be so I can test it.
Thanks