I worked on the driver seat of my 986.2 (2004 Boxster) last week and learned a little about the connections and motor controls. The picture you show does not look like a motor control plug. The motor control plugs on my car can be accessed from the front of the seat and you can even unscrew the 2 torx screws holding the control module to the seat (see red arrow at top left). The power input is indicated by the central lower arrow, and the three motors are powered by the three connectors circled to the right. I assume you could unplug these motor cables and supply power directly to the motors by connecting + to either red or black (forward and reverse) and - to the neutral (white).
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