Thanks Jon. I just finished my seat tonight. You have explained the power issue much more clearly than anyone else. The YouTube video shows the same thing, but it is much easier to look at a diagram.
I took a slightly different approach by using one of the black 5-connector plugs that another board member sold me. Your wiring diagram will be a big help to those who follow us.
Your picture showed the solution to the problem I posted yesterday. If you look at the far left of your picture, you will see a plug with four wires coming out of it. That is the backrest control socket. You can see that one of the wires is gray with a green stripe.
I did not have that plug in the unit I bought. The seller left it attached to the seat back which I didn't buy. (The backrest was in very poor condition and I didn't want to pay to ship it. I also used the seat bottom from my existing seat.) I had to use the wiring that was already in the seat. I cut this connector and the two wires attached to it from the control of my two-way seat:
I used the red and brown wires that remained to power all of the seat motors.
I stripped about a quarter inch of insulation from the end of the wires:
Then I crimped on two connectors:
The crimp-on connectors fit on the terminals in the blank spot on the control panel:
The control unit in my photo is oriented differently than yours. The backrest control socket is on the right rather than the left. When you orient it this way, the gray wire with the green stripe is in the front and the gray wire with the black stripe is in the rear. If you put it in the opposite way, the backrest control operates in reverse of what it should.
You then just plug the connector into the existing connector in the two-way power seat bottom. The existing harness provides power for the motor, so you don't need to make any changes there.
Overall, this was a nice improvement and makes the car feel more refined. The height and distance adjustments are much easier to make than with the manual controls. (The manual height adjuster was particularly clumsy.) One oddity is that the backrest now operates in steps rather than continuously. It is not a big deal since I don't usually make big adjustments.