"Snowbird 583".....To connect the panel to the inverter, many companies used a wiring that looks like your standard telephone connector....the one you plug into the back of your house telephone. On the Magnum inverters which became more popular years later, weird readings on their panel were resolved by unplugging this phone line momentarily and then reconnecting. I don't know enough about Heart inverters to know how they connected them.
Next question, does your inverter work? My neighbor had one that no one could diagnose, so they replaced it and it still didn't work. It kept showing an overload. He asked me to look at it. Just by luck, I checked the large buss bar type fuse and found that it had blown, but still had a small piece of the fuse that was connected. Once replaced, problem solved. The fuse looks something like this http://www.amazon.com/Blue-Sea-Syste...rds=mega+fuses
and is about the size of a large bandaid. It's located on the large 12 volt (+) cable between the inverter and batteries.