So Im also trying to add an ignition on hot wire to a battery isolator. I have a 2019 promaster 2500 without any auxiliary switches. Im looking at the BCM but don't see a large blue wire. I also took off the center console and found the wire under the cigaret lighter but that wire goes hot when the key is partly turned before the ignition turns on. Any other ideas?
To trigger the isolator, I would still recommend the wire in the center console. Why?
1) I'd stay as far away from the BCM-connected wires as possible...if something ever goes wrong, the warranty question will be "what this wire connected to the BCM?"
2) the center console wire is easy, protected by a 15 or 20A fuse, and if it is on when the key is in the pre-run position, it won't do any harm, it just will connect the two batteries - IF the voltage on the van battery is high enough.
3) My Battery Doctor isolator has been connected there for 4+ years with no issues...