It probably isn't the fuse, but it's certainly worth a look. They have a little tool on the side next to the fuse box to help pull them out, at least my 93 wagon does.

It could be the cable(s), but since your's is dead for all motions, I suspect the box under the seat needs some joints re-soldered. On mine, I removed seat (a minor bit of pain, disconnect battery) and undeneath you will find a rectangular black box. This can be opened. I re-soldered any suspect looking joints, and voila, she worked again. Hope it works for you; otherwise, you might try an upholostery shop, they do those things, don't waste time at Volvo dealer, it will cost what the car is worth. Good luck. Mike