Ken Burton wrote on Fri, 11 November 2016 01:58

OK, I think I understand the question now.
The item you are looking at we call a boost solenoid or boost relay.

First is the small terminals. One goes to the thin wire going to the boost switch on the dash and one goes to ground. The polarity is not important, so just wire one to the boost switch on the dash and the other one to engine battery ground. The aluminum plate where the relay/solenoid is mounted is connected to engine battery ground and that is where GM wired their's.

On the big terminals, which side you use there is also unimportant as long as you get the correct together wires on each side. (The three red on the right side of the diagram on one side, and the other two on the left side of the diagram on the other terminal.

One side is engine battery circuits and the other side is house battery circuits. They can not be mixed from side to side. I forget at the moment which side Gm used for which and my coach is not here for me to look at. It will not hurt which side you use for them as long as wires for the two sides are not mixed.

Clear as mud. right?

I will add a few details that might make it a little clearer.

One large post is the house battery, one large post is the chassis battery, one small post is the power for the plunger (goes to the boost switch) and the other small post is the ground for the plunger.

Your schematic is different than mine, so I can only describe mine (which has one more wire on the house battery terminal).

The left side is the chassis battery side. One #4 red wire goes to the "battery pickup junction box" (where the power comes from the alternator through the isolator, through a #10 red wire to the battery pickup junction box, and charges the battery). One #4 red wire goes to the starter. One #4 red wire goes to the chassis battery.

The right side is the house battery side. One #10 red wire goes through a 50A fuse to the house battery bus bar. One #10 red wire goes to the isolator (to charge the house battery) and the #4 red wire goes to the house battery.