As the title states, I need to find a circuit that is hot only when the ignition is on. This has proven difficult because it seems most go hot every time a door is opened.

Here’s the why.
I’m installing a Redarc BCDC charger to charge my dual AGM battery setup properly. Simply tying the batteries together with a solenoid doesn’t give these oversized AGM batteries the juice they need from the smart alternator (been there done that) so I’m trying something new. So far it seems to be working as advertised. However, I currently have the power signal (blue) wire from the BCDC tapped in with an add-a-fuse to the ignition circuit (position 5 or 6 in the under hood fuse block, I forget which one). Even that circuit seems to go hot when I so much as open a door. The problem with that is the bcdc is pulling 25 amps from the starting battery every time we open a door and all the random circuits that draw power go hot, which is less than ideal if that happens all day long at a camp site in the middle of nowhere.

Anybody know of a circuit I can tap that is only hot with the ignition on, preferably under the hood? I’m fine with doing a wire tap, the add-a-fuse is just nice for the convenience aspect but I’ll use whatever is available at this point.

Thank you.

btw I know people like pictures so here are a few of the rig and current “op check” wiring which is not finalized, still need to clean everything up.

 

If I had the electrical manual…. (which I don’t). I would investigate the wiring from the Power Distribution Box, to the Central Distribution Box, to the Auxiliary Distribution Box. And like in my sailboat organize a “house battery” and a “starting battery” solution. My gut tells me the Aux battery should power the Aux box…. but I don’t have the manual…

 

so my aux battery is the “house battery” it’s just being charged by the starter battery and solar through the Redarc BCDC DC-DC charger. The Redarc has a “signal” wire that is supposed to be tapped into an ignition circuit to only allow power from the starter battery to charge the house battery when the vehicle is running or when the ignition is on. however many of these circuits that would only be live with the ignition on in a normal vehicle are “primed” when you open the door of the lr4. So the signal wire is being told to open the circuit to the starter battery and pump 25 amps to the house battery every time I open a door. Not ideal

 

Yes, I catch your meaning. I’ts like a a marine isolator or a battery switch, but not isolating?