Correct, I just replaced the unit. Very similar symptoms, the one symptom that convinced me (and the helpful Magnum rep) that it was bad was the Amp reading. It was obviously wrong when in use and it was holding a constant 26 Amp reading with everything disconnected. I changed out the unit and all is now well. Suggest you perform the same test, disconnect all loads and see what the Amperage reading is.
“Flint” - 2016 SMB Sprinter 4x4 144" RB 150S w/ PH