OK I started this thread I should update it. upon doing further checking I find that the camper battery only gets charged when plugged into 110VAC. The old battery was shot and I have no room for 2 batterys, I installed one 120AH AGM battrey. I wanted to be able to charge it with the truck Alternator.
I wired a 40Amp fuse with 6 guage wire to an anderson plug which goes to a charge relay then to the battery. I am a sailor and had much of this left over from a boat refit. The anderson plug I got on Ebay a bit of overkill as it is good for 100 amps they are quality high amperage connectors
Fuse at truck battery
No picture of Charge relay. It is a m-ACR from blue sea systems it monitors the voltage and closes at 13.5 volts ie: when the truck is running and charging