Anytime i read some has just hooked their battery I have to fall back on did it get connected correct;y.
Find the word "NEG" or symbol '-' printed on the battery case and hand trace this battery cable and make sure it is the one that goes to the TRAILER FRAME GROUND close to the battery.
If it has been connected wrong you may also have three other FUSE locations that needs checked.
There may be a in-line fuse real close to the battery that needs checked. There is also two fuses in the 12VDC Distribution Panel that may read REVERSE POLARITY that needs checked.
Once you get the battery connected correctly than replace these possible blown fuses. If you replace them before getting the terminals connected proper it will just blown them again.
Roy Ken