IMHO, either the switch or motor assembly. You will have to remove the door panel to get to either. I replaced the passenger side motor assembly on my wife's 99 GC, an aftermarket rebuild was $75 at AutoZone, plus $40 core. Hopefully is just the switch, much easier! You will have to pull the door (plastic) door panel away, pull straight toward the cabin, I used a 'wonderbar' tool (nail head puller actually), although there is an actual tool made for this job, ask the guys at Autozone. When you go to put the panel back, you probably will need to replace the plastic ribbed standoffs, they also sell those at Autozone. The job took me (had a helper) about two hours, not bad. If you decide/find you need to replace the motor assembly, repost or email me, I will give you the exact procedure I used. Good Luck!