rocmon,
Since you have a HR I'll guess that you have a Magnum inverter/charger. If not how about more information?
The typical HR Magnum has a 30A AC input and 2 20A outputs - I know you said one was 15A??? Since you have AC input and AC output on one circuit that leaves:
1. A tripped CB on the failing output.
2. A miswired wire on the failing output.
3. The failing output is shorted and you can't reset it's CB.
4. The failing output is good and the problem is downstream as in loose wire or tripped/bad GFI.
5. Bad inverter/charger.
To me the testing procedure could be obvious but would like to know what equipment you have.
