We're playing post tag! I edited my first post. If you look at the name on the relay and google the name under "automatic charging relay", you can get a copy of that solenoid's instruction sheet. It is very simple. One post is for the primary battery for starting (although with some models it does not matter which is primary) and the second is for the secondary battery. Another small connector is to ground, and the second small connector is for manual boost start.

It is fully automatic.