I checked the power at the post where it connects and I have 12.5 and when I use my accesory cord with the batterys it clicks on fine
Hard to diagnose without being there. Sounds like you may have a wire routed incorrectly or something.
From the unit, your power cord is hooked to an accessory block I take it? Do you have power at the Accessory Block? If you unplug the Power cable from the unit and meter the pins of the connector, do you have power there?
Is the power cable plugged in tight and secure?
Wish I could be there to help! I hate things like this. My 785c had a lose connector and I had to bend the pins slightly so they made better contact. The unit would shut off if I wiggled it or hit a wake.
Robert