There;s a bimetalic spring inside the relay that as it heats up and cools down makes and breaks contact and acts as an on/off switch. The directional bulbs will provide the grounds when you get it installed in your truck. Just so that you have a load on it, I'd hook one of the output wires to a bulb, and ground the bulb housing to the battery negative. Depending on how output wires you have will determine how it needs to be wired on the vehicle. I may be wrong here since it was a long time ago that I did this, but the 5 wire setup requires separate directional signals in the rear, and the 7 wire setup is wired through the brakelight switch to allow you to use your 2 rear tail lights as directionals like a modern vehicle. If I'm wrong, I'm sure someone has the right answer.
I did the same thing as you are going to do Paul. Disassembled, cleaned, lubed and painted the switch on the bench before putting it in the vehicle. Mike