The Reverse polarity fuses saved more than his converter.
Also a Surge guard WILL NOT PROTECT against this error.. Several others yes. This one no..
At Risk when you hook up backwards are all your 12 volt electronics This includes the controls for Fridge, Water heater, Furnace and optionally the A/C (Some are suspectable some are not. One of mine is One of mine is not)
Some lights as well
Suggestion.. Get a can or two of spray paint,, The little testor's cans are good for this, you can also use nail polish
RED and Black
Red goes on the POSITIVE wires, as connected, over spray onto the battery is acceptable and in fact a good thing
Black on the negative side
WHILE THEY ARE HOOKED UP PROPERLY.