One thing to remember, the motors are just simple 12 volt electric motors. Try to reverse the wires to the motor and see if the switch will move it the other way. The solid brown is the ground, the other wires are the motor power.
This is the wiring diagram for the seats.
And yea, remove the seats, and turn them upside down to see the wires. Just hook up a 12 volt power supply of some sort to test the movement.
The switches are not a great robust design. There are threads on this site on how to spray contact cleaner in there. That may work for a while but in my experience once the seat switch goes flaky it is not long for this world. If it is the passenger seat, just get it into a comfortable middle position, and leave it alone. Tell the passengers to leave the switches alone. Or just replace the switches if you are like me, and require all items of a car to work as designed, if not better than designed.