Mack,
I am pretty sure that your coach came with a Prosine 2000 watt inverter/charger which is no longer in your coach. The Magnum inverter/charger that you have is a really dependable system. I am reasonably sure there is no interface with the original VMS electronics and the replacement Magnum that you have. If you have the Magnum owners manual, be patient while you read it, I think it was written by the head engineer but it does make sense. Hope this helps, Fred