Danger Will Robinson! - you need a crash course in how the drivetrain on your Jeep works - before you break the transfer case!
Here is my understanding without looking for facts and figures on various websites. Please feel free to add or subtract as many know better than I.
2H = Normal driving on roads with good grip - rear wheel drive.
4H Part Time = Centre diff lock - only use on surfaces which will allow the wheels to slip - snow, ice, mud etc. as when you turn corners, the front and rear props, which need to turn independantly under normal conditions, cannot.
4H Full time (not np231) - Use on the roads too for extra grip - allows front and rear props to turn independantly.
4L - Centre diff locked, but much lower geared (typically 2.5 - 3 times).
If in doubt, remember not to use a part time setting on the road, you'll likely mash your transfer case. You'll know you're in part time cus your steering will be b@stard heavy.
