the plug on the seats is a common vw connector, but you could just use spade plugs from your average cheap wiring crimp kit. the red wire is your live/+ve, the brown is the earth/-ve

fuse you want is 20a, factory they usually had a thermal fuse but bog std 20 is fine. to wire em in you could use the ciggy lighter wires, but thats a bit of a bodge. though you wouldnt need a fuse at least!
the better way to do it would be to remove the panel under the dash on the driver side, this will expose your fusebox. if you look above it you'll se a metal plate with spade connections and brown wires, run the earth here. if your car is a 91, the live feed you can take from a group of spades at the top of the fusebox on the back, labled 'Y' in my fusebox faq (CE2 fusebox, look on page 4) if you can see behind. but its easy to spot, there will be at least 2 big chunky red cables going into it.
to release the fusebox there is a white clip to the right which needs pulling downward, and a clip to the left which needs pulling to the left then rotate down and pull it off, theres a locking peg near the top. you'll see what i mean. then you need to push the left hand fusebox bracket leg to the left, then lift the fusebox up and towards you. do this carefully then let it lower down, dont force anything as you dont want to pull any random wires out. then at the top of the fusebox to the right you should see the group of 4 Y spade connectors i mention, put your fused wire in here

i hope all that makes sence?