I finally found someone who made exactly what I need...a basic "plug-n-play" adapter that links an electric seat from any 1994-1998 Mustang (2-Pin) to an electric seat from any 1999-2004 Mustang (4-Pin).
The plugs fit perfectly at both ends but the seats do not move with the vehicle running. I honestly don't not if it's the new adapter harness or the seat itself. We bought the seats several months ago and back then the seller told us the electric drivers seat worked but it was not in the vehicle as he had already put his new seats in it. At this point, I'm trying to determine where I can take the seat (and the new adapter harness) to find out if the motors are getting power and if the harness is wired properly...basically isolating the source to find out which one is not working properly.
Any advice on how to determine which is not working, the seat motors or the adapter, would be GREATLY appreciated!