Test the tcase switch first...
Take off the wiring harness from the switch, it is on the driver side off the TCase sticking almost straight up on top of the case, the wiring harness is a two prong harness.
Turn the Jeep to on, and short the two connectors in the harness together, your indicator lamp should come on. This means a bad switch.
If not it is either a bad lamp, or bad ground.
If the lamp did not go on then short each side of the connector to a known good ground. If the light comes on you have a bad ground.
If the light did come on then check continuity on the terminal that did not make the light come on to a good ground, if no continuity then check the ground wire, I believe it grounds someplace behind the valve cover, I can give more info if you need it.
The switch is about $20 from the dealer and takes about 10 minutes to replace. I was able to get my switch off with a 7/8 deep socket on a 3/8 rachet.
Make sure if you need to replace it that you blow off everything from around the switch, it is a flat area and collects a ton of crap.