I just recently bought an '88 Trooper II. I thought it was a great deal, until I discovered last night the 4wd is not engaging. It has an auto tranny, with manual hubs. The 4wd light comes on, and it will shift into low range, but the front wheels don't pull that I can tell. I can drop the back tires in a mud hole, and they will spin with the front sitting on dry ground. No noise, grinding, or anything to indicate they are not pulling or something is wrong other than they aren't working. I'm new to Isuzu, so patronize me in explanations. Is it something simple, or has my good deal gone bad? Any suggestions? Thanks.