You can get complete wiring diagrams for those vehicles by going to the Mitchell Manuals website (referenced below). They charge $9.99 per vehicle for a one week subscription to their database. Their wiring diagrams are more detailed and complete than any others.
I would expect that you could just use the 1999 diagram to find the power and ground wire connections at the seat; and run a power wire to the seat switch from the cigarette lighter or the battery "+" terminal. The cigarette lighter should already be protected by a fuse; but a power wire coming from the battery should be routed through an added inline fuse or circuit breaker of appropriate amperage. This would probably be much easier than trying to tap into the fuse block, or cutting harness wires.