There are two thing that are probably going on
1) You probably need to clean the switch contacts. There are a lot of write ups about this.
This is the best write up that I have seen. It may be a different car but they use the same switch.
www.rangerovers.net/repairdetails/seatcontrols.htm
2) The wires from the switch to the seat break at the door hing. I had to splice in new sections of wire at this point on my drivers side.