I can't get the landing gear to extend or retract. Before considering that the motor may be burnt out, is there a fuse serving this circuit? I took a look at the breaker/fuse panel but can't see any fuse marked as serving this function.
Back in that era of cruisers it was common for some of us to break the wires going to the motor and add a separate switch in the front storage compartment. This was done to stop/discourage the tampering with the external landing gear switch. Which as you know is located on the OUTSIDE of the camper. It's possible you have acquired a unit with that extra switch.
Look in the front storage compartment--find the motor for landing gear, and then the wires and trace them back thru the compartment and see if there is such a switch.