Check your distribution center for usually two FUSES that are off to them self labeled REVERSE POLARITY. These are two fuses along with the single in-line fuse you have already checked that are between the 12VDC distribution panel and the battery terminals.
The batteries should also power up your inside ceiling lights when you are not using the 120VAC shore power connection. i.e.if you are disconnected from the shore power connection you should see the 12.6VDC coming from the charged up batteries at the same point where you measures the 13.6VDC when you had the converter activated.
If you don't see the battery DC voltage at the 12VDC distribution panel then you have blown fuses, bad connections, dead battery, or perhaps an installed battery disconnect switch in the OFF position.
Has any work just recently been done on the battery terminal which was removed. They may have been installed in REVERSE ORDER. Find the word "NEG" or the symbol "-" on the battery case and make sure the cable connected to this negative battery terminal post comes from a FRAME GROUND connection which should be close to the installed battery. This is about the only thing that blow the REVERSE POLARITY fuses.
Roy Ken
