I think I would disagree with that solenoid being the battery disconnect solenoid if there is coach on one side and chassis on the other?? The battery disconnect switches, if we have them act to operate a relay but there is one relay for coach power and if we have chassis disconnects, that requires a second switch and second relay as the disconnect switches will only act to cut off power to one of the two systems, chassis or coach, not both on the same relay!
I think if you are finding a solenoid (different name for relay due to shape!) and it has cables for BOTH coach and chassis power, that will be what is called a mode solenoid in the later years.
Some guesswork involves here as I am unsure what year they started stamping ID on the smaller wires? But if you find the ID on a small center terminal on this solenoid, that is likely wire LR if it is a three post solenoid. If it is a 4 post type, there should be LR on a center post and another small post where you have wire FM. Two types of this solenoid were used at different times, so guesswork on which you may have but both work the same. When the dash switch is flipped to connect the two 12Volt systems together, 12VDC is sent to the small post on LR, goes through the internal coil either through the metal case if 3 post type or to the metal mounting screw.
Depends what you see, 3 post or 4 post type. The idea of the 4 post was they stopped depending on getting good ground only by the mounting screw and started using the screw PLUS sending ground on FM, belt and suspenders type planning!
But both types have a common problem in that the contacts inside arc every time they close and tend to burn and corrode quicker than we like!
But a test is easy if we have a meter. Put one probe on a ground point of some sort like the frame, etc. and the other probe on each side of the big side lugs. Likely you get a slightly different reading from the chassis than the coach?
Now flip the dash switch to connect the batteries together and the voltage should match on both sides! If you hear the solenoid thump but the voltages on left and right side don't match, you may have burned/corroded contacts inside!
If in a semi-quiet place, try flipping that dash switch and listen for the thump from this solenoid? This is not the normal tiny contacts but more like slapping a silver dollar on the lugs to get a good noisy "thump"! I work it by trying to hear the thump and THEN check the voltagesa are passing through?
But an even more common problem is corroded cables between this point and the two battery groups!
But you can compare the voltage on ech battery positive post just as on the solenoid!
If they show l slightly different voltages and then the same when the switch is flipped to connect them, you are getting it right!
Connect them together to charge as you drive BUT be sure to flip the switch while camped or you WILL risk having both batteries dead when you want to leave!
On generator starting, I would suggest first get it to crank well when the RV engine is running and the switch is connecting both coach and chassis battery supplies togehter as that gives the best, most sure way.
It shouod crank pretty much like a car engine. Good and steay but often four cyclinders and sounds different than cranking an 8 cylinder? But if it ias getting good power to crank, it shouold crank good and steady as long as you hold the button if it is getting power from the engine alternator!! Not to crank it terribly long enough to overheat the starter, though!
Idea is that as it cranks, there should be fire going to the spark plugs and fuel to the cylinders where those plugs are firing! But first the engine has to be cranking good to make the fuel pump get fuel and the plugs get spark!
Just about everything on the RV, does batter if it has good power getting to that item.
On and old RV that has set for a while corroded connections on the cable from the battery to the generator can be a problem, too.
thank god 
... and there is fuel in the line which im guessing points to the fuel pump... seems like its not getting power to me...
