You are not likely to find a wiring diagram. If your house batteries are not getting recharged; you have a charging circuit issue. If you suspect the loose wiring will charge the batteries, check for voltage from them when plugged in or the generator is running. A ground wire will, or should have zero ohms resistance to the frame of the coach. Connect ground to - and positive voltage wire to + post of the battery(s). If the dead battery is the chassis battery, then you will need to use something like an Echo charger so the batteries are not directly connected together.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7