.

There seems to be something unplugged.

This

IMG_1607.jpeg


Those two connectors both have a marked on them. It really looks like the wire match up. With two controllers, one would operate the front tires and the second controller, the rear tires. This connector looks like it pairs the two controllers together. Since the marriage is lost, only the front tires move.

Before you plug these back in, I would double check that the color wires would match up. I believe this is your issue.
 
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