Okay, we can start with what we see.
Some confusion but we can get the ones we do know out of the way.
View attachment 2415962
Top left is the ground buss bar where which is one main place where ground/negative wiring goes. I think I see it is attached straight to metal, that tells us negative battery cables go here. If coach batteries are in different location, there may be another bare on metal frame where those go!
Part two at right is called a mode solenoid. Different name for a relay pretty much because of the shape and way it moves but a set of large contacts that close when battery and ground are put on the two small wires. I might guess the small green wire to be ground but test that before trusting tooo far! RV colors are not always the same as other wiring and several of your cables have been changed and not "normal" colors!
The idea is there is a switch near the dash usually and in your year RV, you could turn that switch on to send power to the coil in the solenoid. That power goes through a coil to make an electro- magnet close the contacts that connect the chassis positive to the coach positive to let power from the RV engine alternator charge both the chassis as normal but also the coach batteries.
I see a change in names!!! I use coach for the battery feeding RV stuff like lights inside and fans, water pump, etc. The chassis for the normal car truck/ stuff. At this point they called the RV one "aux" battery, a old name from boats!
Read over page 36 of that owners manual to get the idea of the "dual battery switch"? Turn it to dual and it stays as you drive but then when you camp, you want to turn it off to separate them to avoid running both batteries down to be dead for starting!
Hold the momentary side while cranking if your start battery is weak and that gives you a jump start from the coach/aux batteries! Jump start without getting out the jumper cables?
View attachment 2415962
What's under that black cover at lower right? First thought was AC plug but not if it connects to a battery post clamp??? Any chance that is actually a clamp with a black over and the battery clamp we see goes to the positive of one coach/aux battery and the black cover goes to a second Aux battery positive post?
That looks kind of home-made so if you have aux batteries in some other location, they may have thought to add more batteries here?
I don't like the idea of not seeing any clamps or ways to tie more batteries down but we can find some strange things at times.
Let us know if any of that makes sense? My suggestion might be to start with getting the starter and RV engine going as a first set of cables and then the second set for the RV things may get less confusing!
You should have the normal auto type 12VDC, then the RV/aux 12VDC and finally there will be the 110VAC that has a form of charger, often called a converter or load center.
That last part should have a big cord to plug into an outlet. that feeds AC to the charger/converter/load center, depending on what name they used. That charge system feeds the RV electrical as well as charge the aux batteries.
You got lots of confusion when first starting and it is not in the best of shape, so we may have to wander around a bit while we try a few guesses.
and pick things up fast. Just need some guidance. 
