Use a multimeter to check continuity from the big ceramic resistors to wherever they connect elsewhere on the board.

I had a problem with Red's mouth working intermittently, and after way too much troubleshooting, I realized that the leg of one of the resistors was just resting against the where it had broken off. I resoldered it and was perfect after that.

Because you had to replace the resistor, I'd say it's worth looking in that general area.

I thought there might be switches, but I checked the switch matrix and confirmed there are not.

The mouth motors have a special board that can drive the motors in both directions. (See schematics from manual below.) It runs either direction briefly, and assumes that the movement has been completed.

Note that this is fundamentally different from the bulldozer motor, which only runs in one direction but has switches (switch 12 dozer down, switch 15 dozer up) so it knows where it's at.

road-show-mouth-motors.png

If they're wired as solenoids, I don't think you'd need a logic probe, just a voltmeter.

But don't assume I'm right without a second opinion.

Mmm.... both?