The light should come on but in the event of a light malfunction, you'll know if you're in 4WD by the sound of the drivetrain. More of a rumble with it when engaged.
With the 242 transfer case, you can use fulltime 4WD in any road conditions, even dry pavement. Part time should be only on roads that provide some slippage.
Be sure to verify that this vehicle works in all 4WD positions, as well as ensuring that everything else works, before making an offer.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!