As said above. The converter has a set of fuses (some have 2 others have 3) that blow if the battery is connected reverse. In most cases the black battery wire is positive (brake wire is blue) and white is negative. But not always.
On my 2010 Jayco 23B the battery connections are white/black but inside they used orange, black, and red for positive. You need to follow the wires from the battery to the the converter to be sure which wire goes to which terminal. Newer jaycos with LifePO4 batteries used the more traditional black (negative) red (positive) colors.