DP Charging Problem

Thanks for the info from all. Will check the sense line and other connections to alternator if I can reach them. Can see the alternator from rear door but can barely reach ; not sure how I will check the connections but will try. I know where the sense line connects to battery. Have a diagram of the isolator relay but not sure where it is. Diagram says "Rear Electrical Center". Don't believe its the electrical where AC power comes in?

Battery is not the problem. It charges from coach charger when engine is off, then cranks engine ok.