I'd thought the problem was the Battery Disconnect Relay. Our Jayco has one battery Ground wire, but about Four on the Positive. I've had failures at the connectors there too. Suggest once you know it's all working properly and all the terminals are good (I ended up fixing more than just the one that came off), then...
1. Tape all the Positives into a bundle with electrical tape so you know you don't miss one when you clean terminals, change batteries, etc. Same for Negative if there's more than one.
2. If the Battery Terminals use Wing Nuts, replace with Stainless Lock Washers under Stainless or Brass Nuts.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB