[Richard]

Here is what I can tell you about the setup, and I have never seen the relay you are showing.

The black (hot) and neutral (white) are wired into the well pump switch, the square D box to turn the pump on and off based on pressure. The square D box is a standard well pump switch. The other nondescript grey box is more interesting. It is a relay triggered by the HWH leveling system. It turns the compressor on. The interesting thing is the HWH switch is wired parallel to the well pump switch. Either will turn the compressor on. The HWH relay, being wired in parallel bypasses the well pump switch so that the compressor will provide maximum pressure. After all the well pump switch is ususally set at 90 psi cut out, which is not enough pressure to raise the rear of a the coach.

All that to say, find your hot and neutral wires. Wire them in parallel through the well pump switch and the HWH relay to power the compressor. Forget about that unidentified relay..