Please explain "Part-time" 4x4

Could somebody please explain to me what the Part Time function on my 1995 XJ Sport with 242 T-case means?
I've noticed that when I shift from 2Hi to 4Part Time a light on my dash comes on saying part time. Well when I shift from 4 PT to 4 Full Time the light stays on.
I'm just trying to figure out how this t-case is supposed to work. What 4x4 positions are recommended for which driving conditions...
2 HI= Highway
4 PT= Ice, snow?
4 FT= Mud, sand?
4 Lo= the real bad stuff?

Is any of that right?
Thanks for any information!
Jason

Part time: locked differential between front & rear axles

Full time: LSD between front & rear.

Part time shouldn't be used regularly on dry pavement because the geometry of a normal turn needs the front & rear to turn at different speeds. Either the tires chirp (slip), or the drivetrain flexes. Neither is healthy for daily driving.

Full time can be used on dry pavement, because it allows slippage between front & rear.

I use full-time when it is icy out, or when we get rain after a long dry spell and the roads are slick.

Sounds like the part-time light is staying on when you shift from part-time-hi to full-time-hi - it's probably nothing. If you are putting it into part-time on dry pavement, the binding effect may be the problem, also check that your tires are all inflated correctly, and the transfercase has plenty of fluid (it does not share fluid with the transmission and the lube places never check it).

Personally, I go from part or full-time-hi to 2-hi - jam it all the way down, give it a little gas and let off. The only time I had trouble because of a low tire, I had to put it in reverse and back up a little bit to get it to go. Part-time-lo requires you to stop and put the transmission in Neutral. Hi ranges are "shift-on-the-fly"

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