I have a 1994 cherokee and I recently got a new backup swiitch and all was fine. Now the lights only stay on when I hold the shifter between park and reverse. Is there a switch on the shifter inside the car, or under on the trans somewhere that needs to be adjusted?

 

Just the NSS as far as I know>

 

The NSS (Nuetral Safety Switch) is located on the passenger's side of the trans itself. If not properly tightened when first installed...it can become misadjusted.

Have a friend or something highly reflective behind your XJ.

1. Set parking brake. Blocking of tires is not needed but a good idea.
2. Turn ignition to the "ON" position but DO NOT START.
3. Place shifter into the REVERSE position.
4. Take a 13mm box-end wrench and weasel your way underneath.
5. Just above the trans pan on the side of the trans housing you will see a unit with a big trunk of wires going to it. Its held in place by a big NUT and a small bolt. Loosen this small bolt. (IIRC its a 13mm) DO NOT mess with the bigger one.
6. Carefully pivot the NSS (pivot around the BIG nut---not the one thats laying under the Cherokee.) Until your friend hollers the lights are on or until you see the reflection.
7. Good idea to find the range of pivot that the lights are lit and rotate to the center.
8. Tighten the small bolt.
9. Crawl your butt out from underneath (For ME this is a step in itself)
10.Run shifter thru the gears to make sure the lights ALWAYS light up when they should.
11. Place in PARK and try starting. If it starts then you have adjusted it correctly. If not, guess where you're going AGAIN.

I hope this quickie rundown is helpful.
Sometimes it make take two or three "tries" Maybe you'll get lucky and nail it on the first shot.