Wiring a 12 VDC charge line from coach to toad is really not complicated:
From coach end, inline fuse, 8 gauge wire to 40 amp RELAY, 8 gauge wire to connector, same on toad end-- 8 gauge wire to fuse located at the toad battery.
"Trigger" to close the relay is coach IGN on.
Also 8 gauge ground wire in both vehicles.
Now anytime the coach ignition is on, toad battery is being charged. Ignition off, no connection.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240