Hi, JD,
My equipment consists of a solar controller, a shunt and the dc to dc controller. When the dc to dc is disconnected at the andersen connector from truck to trailer there is no bluetooth blue light on the controller...nor is it discoverable. When I connect the andersen ends together it then becomes discoverable with no charging as the truck is off, but it does indicate truck battery voltage. Texas is one windy place :)
Onward,
John