Thanks all, I will try to find a part number on them which would then perhaps lead to the specs.
It could well be an add- on by the RV builder and not Ford. Good point. The regular E350 van seems to have an aux battery over on the driver's side that uses a similar set -up, but my RV does not have any aux batt, just the house battery bank farther back in the Rv part.
The whole thing starts with a pos wire ring terminal on the starting battery (passenger side) post clamp, then to the solenoid near that. The solenoid has the wire from ignition via EEC relay to power it.
It all works the way it is supposed to thank goodness, but more amps could be useful at times depending on the scenario.
I have not yet tried the trick with an inverter on the starting battery powering a battery charger on the house batts. That method is available if parked and the engine is idling and means no change to OEM set-up. But not possible while driving so upgrading the OEM set-up would be needed for more amps that way.
