On my 98 Sport, it came with basic seats that were broken. I found some really awesome power seats with lumbar out of a 99 model in the JY. Anyways, I could not find a harness or wiring under the carpet or in the cab when I pulled the seats and carpet out to do the install.
What I did do is run a new power wire from the fuse box, under the carpet to the seats. I grounded the "ground" wire on the Power Seats to the body. It is really easy and quick on the update and install!!!