Is the converter working is easy to figure out.
hook a DC voltmeter (15 or 20 volt range) to the batteries or to the fuse panel so it is showing system voltage.. DO THIS WHILE YOU ARE NOT PLUGGED IN and use caution as the batteries are still live
NOTE the voltage
Plug in.. Note the voltage
Come back in an hour or two and NOTE THE VOLTAGE
Post the results and we will tell you,
There are better tests but... For this test... YOu do not need to know WHERE teh converter is
Finding the converter
Many are right in back of the breakers and fuses. this is especially true if the fuses and the breakers are in the same "Box" IF yours is like that the make and model of said box please.
Otherwise it has a small fan you may be able to hear, also indicator lights in many cases.