I will be the first to say that I am not to good about 12v. systems. I would first check the on/disconnect switch. When you use the switch you should hear a click. If you do not hear a click you may have a bad selanoid value. There also may be some breakers just off the batteries that could be tripped. Sorry not to much help. Maybe someone who is better on 12v will help.
Retired and never looked back