BrocNeal,
OK, look at the schematic on page 20 of the maintenance manual. You will notice the SCR in the upper left corner of the schematic. The SCR acts like an electronic on/off switch. How the system works is that the battery charger PC board monitors the charge level of the house battery(s) by inputting the current battery voltage level onto the red wire going into the board. The board analyzes this voltage level and determines if further charging of the battery(s) is necessary, If so, the board sends a signal to the SCR's gate terminal via the green wire shown which then turns on the SCR connecting the output of the DC voltage output of the transformer module via the blue wire shown into the SCR and since the SCR is now turned on the SCR now conducts that DC voltage to the output terminal of the SCR which connects to the battery9s) via the orange wire.
Actually, the SCR is never fully turned off. The charge board varies the signal to the SCR gate via the green wire on a pulse basis with the turn on pulse being longer when the battery(s) are heavy discharged to a turn on pulse being shorter when the batter(s) are fully charged and only requiring a low level maintenance charge level.
If this SCR was destroyed when the former owner connected up the battery(s) reversed polarity, of course the charge board would be trying to turn on the SCR to try and make it conduct a charge current to the battery(s) to no avail.
