Quick mod to maintain engine battery from solar supply

That's interesting, but the relay in my C that connects chassis to house 12 systems is not in that box. It is a lot bigger, more like a starter relay.

I have that relay slot in my passenger van, but no relay in the slot, because it doesn't have the towing package.

Use of the towed vehicle charge circuit to charge motorhome house supply is kind of neat, intersting that one manufacturer uses it, but for many C motorhomes the power draw will exceed the ratings of that circuit.