2012 freightliner cascadia dd15 help

Have you ohmed out the cables? Seems like the only piece of the puzzle

 

First, go to the alternator and make sure you have 12.5 VDC at the alternator charge post with the truck off or that it at least matches battery voltage. If not or lower than battery voltage you have an open(bad connection) between the batteries and the alternator. With no voltage @ the alternator it will not begin recharging the batteries.

If that checks out, start the truck and recheck the voltage at the alternator and batteries to match at or around 13.5 to 14.5VDC. If that checks out you have a bad connection between the batteries and the cab.

 

No problem. Dont get to see FL at all so not sure where to send you from here as far as common problems. My next stop would be fuses and breakers. Start measuring at other locations to see where your voltage drop is. Did you clean all the cables and connections with the new batteries?

 

Not sure about your cascades, by the Coronado’s (FL122sd) of the same year have a fuse box (PDM) mounted on the front top left outside of the cab fire wall, from there it travels over the engine to a post on the passenger side firewall (@6ga cable going to a bolt with a red insulator). Opposite of that on the inside there is a cable that runs up the the main fuse panel, and that’s as Far as i’ve Ever gone. But follow your cables and make sure they are good and clean. Use your volt meter and check the drop over each of those connections.
I have also seen fuses crack and cause this so be sure to check those also.