After delving into your problem, I have the solution. Progressive Dynamics 9200 series 45 amp deck mounted converter with charge wizzard.
I do not believe that they make the 8800 series converters any longer and my guess is that the 8800 series was a failure. Too many problems just like yours. The thing is not reliable and you need to replace it.
If you have a battery disconnect switch, check the operation of that. They do fail and usually in the normally open position, why I don't know and I'm not going to try and find out.
Your converter is toast.