I had a 94 before, and that is exactly what I did....
The power seat and also the cig lighter in the console did not have power. It was eventually traced to the classic mustang problem in the ignition switch. I chose not to spend the 500 clams to get it taken apart.....
So, I ran a hot wire from one of the empty fuse locations directly into the switch in the seat... that baby worked like a charm once I figured out where to wire it into.
What I did do, just for fun, is to put an actual fuse in that slot and run the hot wire from the downstream side of the fuse, if you know what I mean, and also bought one of those inline 10 amp fuses which I installed just to keep it from shorting out and bursting into flames or something....
But, clearly, as long as the slot is hot, which it probably is, you can plug anything you want in there.