Hi all,
I ran into this issue a while back when I was deep cleaning my xk8 for the first time. I was moving the drivers seat back when the whole seat turned off. Seat heater won’t work, and seat won’t move. It seems as if a plug disconnected, but I can’t see anything out of the ordinary under there. Is there a main cord supply under the carpet I should check?

 

I would remove the seat, disconnect the electrical connectors under it, spray them with electrical contact cleaner, and reconnect. In my wife's 2006 XK8, each seat is held down by four black Torx T-40 bolts (one in each corner of the seat rails)....

 

Standard approach is to swap driver and passenger control modules, assuming one works and the other one less so. The modules are located under the seat bottom, near the front ledge. If functionality is restored with a module swap, it is just a matter of repairing the circuit board. The short of it is that the board is loosely mounted in the hard plastic case and vibrations end up breaking track connectivity at the edges. The fix is to solder shunt wires. These modules normally require "pairing/coding" to the car for full functionality, so repair is considered the best path. There are tons of posts about this, this is a common problem.

Best of luck, keep us posted.