Heated seats. This is a common problem with Grand Cherokees. I took mine to the dealer and they sent it to an ulphostery shop to remove the seat bottom (they were afraid they'd ruin it) and they ended up replacing a thermister that was defective (open) with a 1 ohm 1/2 watt resister. Wala it works. Anyway they make a repair kit that supposedly doesn't require you to take the seat apart. Here's the link to the TSB on my Web site:
http://home.sc.rr.com/janet/TSB/08-03-99.htm