I took the non-working contactor apart and saw the problem immediately. The wire from the 'In' hot line had come loose from the solder joint on the inside of the case. I soldered the wire back on and all works as expected now.

The new one should be here in a few days, so I will keep it as a backup.

They really are a simple/ingenious device. Two solenoids to press on spring loaded contacts. When no voltage is applied to the control wires, the spring loaded contacts connect both winch lines to the ground line. When voltage is applied to one of the control wires, it activates the solenoid, pushing up one contact so that it disconnects from the ground and contacts the hot side.

Pretty cool how it works, IMHO.

Thanks for the replies, guys!

 

Now you have a spare! Glad you didn't just throw it away. Good work!