Wiring on PAR/Jabsco pump?

[Deezul1]

I have had this pump laying around for a while and am not sure of the wiring setup. I know the Red unit is the pressure switch. What is the green unit? There are 2 black wires coming from the motor, 1 of which goes to the pressure switch and I believe the other terminal on the pressure switch is the + or positive feed input and the second wire would be the - or negative lead. The green thingy has me puzzled. It is fastened to the pump base but not plumbed into the pressure chamber.

TIA

John