Hey there!
As a quick temporary fix - unplug the fuse.
There should be a bank of fuses behind the glove box or under the dash. It'll give the location in the owner's manual if you can't find it. Near the fuses you'll see a diagram showing what each fuse is for. Unplug the one for the interior lights, and that'll give you time to solve the actual problem.
Use a pair of tweezers if you can't get your fingers around the fuse to pull it out. Be sure to pull the fuse straight out.
Lots of Wrangler owners' simply unplug the fuse for the interior lights when they take their doors off.. It's a simple, easy free solution (that's what we do - we leave our doors off for weeks at a time).
The problem is probably very minor - and Jeeps are very easy to work on... Don't worry and tell your brother congrats on joining the Jeep family (expect a few waves).
This video is just to show where the fuse box location is:
Here is what each fuse is for in a WJ
https://cimg0.ibsrv.net/cimg/www.cherokeeforum.com/1015x501_85/612/Fuse-Labels-90612.jpg
Looks like it's fuse #16.
...it's really just a temporary fix (that lots of folks do) - but it'll save your sanity while you're looking into the actual cause!
Someone else should be along with some knowledge on what the issue might be. It's always a good idea to cross-check the advice you receive (you should be able to find multiple instances of folks with the same problem and solution).
Oh - and if you're going to dig into anything electrical ALWAYS disconnect the negitive battery cable (unpluging the fuse is ok).
