« Last post by mikeh on Today at 01:25:52 am »
I was going to post a wiring diagram that Randy Hyde had posted here about a year ago, but I see that CalCruiser beat me to it. That diagram was for his 2008 2350, so should be fairly close to your original layout. There have been some minor changes in Phoenix Cruiser wiring over the years, and different components used, but the battery isolation solenoid you refer to has been pretty consistent. As you probably know, the purpose of that solenoid is to connect the the house batteries to the Ford engine battery (when the solenoid is energized) to allow the alternator feed to also charge the house batteries. The solenoid is energized when the key switch is turned to "ON"; the rest of the time it is de-energized, isolating the engine and house batteries from each other.
Wiring, as I said, can vary slightly--but basically the wire on one of the big solenoid posts connects to the (Ford) chassis battery as you noted, and the other big post feeds a 40-amp self-resetting circuit breaker (the thing you call a fuse) and from there that wire runs to the house batteries. The two small posts energize the solenoid. One goes to ground, the single black wire that you noted. The other post has at least two wires--one is a feed from the "ON" circuit of the key switch which energizes the solenoid when you turn the switch on. That wire doesn't normally come from the key switch itself--I believe on my 2019 rig it comes from a terminal in the under hood Ford fuse block that is energized with key-on. The second wire, as you guessed, feeds from the "white switch". Depressing the "white switch" allows you to directly energize the solenoid (if your Ford battery is dead) to connect the chassis battery with the house batteries to slowly back-feed some charge into the Ford battery from hot house batteries. The "white switch" gets it's feed from the house batteries--frequently by tying onto that 40-amp breaker under the hood (that second wire on the other side of that breaker you mentioned is likely your feed to the "white switch"). You also mentioned in your application a third wire on that small hot solenoid terminal--I'm not sure what that is; most likely it is picking up a key-on 12-volt feed for something, since that post gets hot when the key goes on.
I have not done a lithium upgrade on my unit yet, but in reading posts here from those that have the usual process when installing a DC to DC charger seems to be to simply disconnect the solenoid system. The main wires could be simply removed and taped (insulated)--that would effectively eliminate that system. You would lose your ability to back-feed charge to your chassis battery by use of the "white switch", but there would be no other problem. If you leave the solenoid and small wires attached--even that third wire feed would still be active for whatever it does.
Best of luck, Mike