ok that relay thingy you are showing is called a contactor. 
its bassically a switch. 
on the left side of the contactor(on your pics) you have the LOAD. 
all you have to do is run your 2 wires(LINE) to your poles(the screws you were talking about)one on each side 
and then run the ground wire to the frame/chassis with the other ground. 
the wires on the side of the contactors is what causes it to ''pull'' to come on 
(via a pressure switch im sure instead of a cheap lever like mine) 
it will make it easier to understand how the switch works if u remove(temporarily) the little cover so u can see exactly how the contactor works. its really easy 
IM me if u need further assistance @ v8dats