I haven't had much time to work on this, but I am finally getting back to it. I was able to source a plug to hook up the power from another board member. I'm using a computer power supply to provide 12-volt DC while I have been experimenting.
I have puzzled out most of this and have the base of the seat working. My only remaining issue is the operation the recline function of the back rest. I need to adapt the wiring from the two-way power seat to work in the full-power seat.
As I stated in my first post, the plug socket on the far left of the control box for the full power seat is for the seat back recline function. It appears that on the original installation, 4 of the 5 available connections in that socket are needed. Two of these are for power. Two would be for the control. (In this case one of the signals would be for forward movement and the other for recline.)
Based on the wiring in the other plugs, it appears that the two smaller diameter wires are for power. (The red wire brings the power from the power source and brown is ground.)
From what I can tell, the seat back motor (which is from my original two-way seat) is already powered from the existing harness in the seat, so I only need to hook up the controls.
Here's a picture of the control for the original two-way power seat:
There are 4 wires which I think are:
Red - Power
Brown - Ground
Grey/Black - Control - Forward
Grey/Green - Control - Back
I think the power and ground are needed just to power the switch because the connector leaving the switch has just two wires - Grey/Black and Grey/Green. The motor power and ground must be on another circuit.
I am hoping that someone can confirm my detective work. My next step may require cutting some wires and I while I will do it in a way that would allow me to put them back together, I prefer to get it right the first time.