I've just gone through this, fixing the entire electrical and lumbar system.
I guess, my first question is, why would you suspect the wires underneath if you haven't messed with them. have you changed them or been in there? If so, yeah, you hooked power to the driver's seat only. I did the same thing when hooking mine up and it displayed the same symptoms, but I would think you've been in there to hook them around the wrong way. The plugs are easy to interchange.
If you haven't been, then you're back to looking at your switch. That is a problem as the switch does not come out easily. But, the good part is that the left side, power seat, not lumbar of the switch,
interchanges with other switches. You just have to undo the circuit board from the bottom of the switch. Or, get another switch with lumbar though they are expensive. Finally, another way to test is getting a normal switch and hooking it up. All that is cumbersome and expensive though.
Ralf
Try to see what's going on with your switch first.