Er, yes it would be compatable, except that you only have half of the wirng harness. The other half would have the blue/yellow wire a ground wire, and the leads to the seat heaters(I am assuming the half you have goes to the switches). If you had the other end you would just have to screw the black wire to a ground point, and hook the positive lead up (blue/yellow or blue I think) to the fuse box. I'm thinking your heaters should have worked on the #4 fuse. Are you sure your wiring is correct?
I would not worry about taxing the electrical system. The fuse will blow if you overload a circuit. It would only be dangerous if you put a larger fuse in an existing circuit to stop the fuse from blowing (some circuits, like the tailights have 18 guage wiring, and I am guessing they should have no higher than an 8amp fuse)