Edit: I see you figured it out while I was typing. Good luck.
The relay is triggered off 12v, you can see it on the picture. It is a 24v relay that can handle 8A at 250v although this is way more than necessary for this setup. The board is just a standard breadboard. You can get them at Radio Shack if you still have one near you.
He connects the relay in parallel with the trunk motor. This way when the motor is running it energizes the relay. When the relays is energized it opens the contacts for the eddy board, which means no ball hits can be sensed.
Connect the relay's coil contacts to Pins 1 and 4 of J2 on the motor control PCB. This will allow the relay to energize when the trunk is moving.
Now hook up one lead of the eddy sensor wiring to the normally closed contacts of the relay. These contacts will be opened when the relay is energized by the motor so that it can't sense a ball. The wire you want to run to the NC contacts of the relay are Pin 2 on J1 of the eddy sensor PCB. You are basically running this wire into one NC pin on the relay and back out of the other NC pin and back to the eddy board.
The connectors on the breadboard just pass the power either to the relay, or directly through from one pin to the other.