OK! That leads me to think it possible you really don't need to go to that trauma of getting the solenoid out!
But that's still possible, so I suggest maybe do some testing first, as it sound more like there "might " be a problem with corroded cables or something that doesn't need a full blown back breaker!
When it kills the chassis battery cranking when the switch is pushed, it seems to say you are connecting a really dead coach battery to a good chassis battery!
Got any ideas if the coach battery is good or if it is really , really, run down dead?
That solenoid has two times when it should connect coach and chassis and you can use that to do some testing.
One is like you mention and pushing the switch does it. But the other is when we drive it should connect them as a way to get charge from the engine alternator to both the coach and chassis batteries.
But we probably can't hear the solenoid move while the engine is making all that noise!
One kind quick test is if somebody is standing close to the solenoid. Maybe even have your head in the compartment, while somebody pushes the button?
It is a big set of contacts and it is possible to hear it "thump" if it closes??
that can be step one as it tells you the wiring and coil of the solenoid is good.
But step two needs a meter to watch the voltage on the coach battery when the engine starts and connects the alternator for charging!
First step and hearing it move tells you the controls are closing but it doesn't tell you the contacts are not burned too bad to make contact and pass what the alternator is doing over to the coach batteries!
If you get the thump but not the charge, THEN you may have to get in the compartment far enough to get some contact with the meter probe to the big lug on the side of the solenoid. Maybe you can get an arm in far enough? Or maybe you can bend a hook on the end of a nice stiff wire to "extend" the meter probe far enough to check the voltage?
I try to find the easier way to test things, so first a meter on the coach batteries to check voltage may save some trouble getting into the tight spot?
If you let the RV set for a bit to let the batteries get stable, then check the voltage of the coach batteries, you can then start the engine and expect to see the coach voltage go up once the engine starts if all is working right. Revving the engine should show that voltage go up and down! But if you don't see that, it says the path from alternator to
coach is no good! Maybe the solenoid is a problem or maybe the cables are corroded?
So you may have to figure a way to get the meter connected at least long enough to check the voltage on the coach side that should go to those batteries.
Being sideways in the compartment makes it harder but the solenoid should be the item closer to you at the RV side.
View attachment 1324935
If things are not changed from when built, the big lug closer to you, should be the chassis battery and the other side the coach battery. I marked those as red and green on this drawing.
There should be two small wires, one tied to the mounting screw is ground from the front and on the center small lug is wire LR which brings battery down to operate the solenoid to close the contacts! If you don't hear or feel the solenoid thump when the switch is pushed, check these small wires for battery on the center lug and ground on the other small wire.
But if you feel/ hear it move, then the left and right sides should show the same voltage as they connect together inside!
If you see the same voltage on each side when it connects but not seeing it at the batteries, then there is a problem on cables between here and batteries!
The other big part to the right is the coach battery disconnect relay that the disconnect switch moves and should not be involved here!
I'm trying to keep you from having to get in that tiny little space but sometimes my plans don't work the way I want!
Wish you luck and let us know how it goes?
Cross your fingers, maybe?
