I've searched and not found the info I need. How do I wire to charge a 3rd battery when the engine is running, but not be able put any load on the truck's batteries when the engine is off? I could wire something into the trailer charge wire, but it is my understanding that that wire is always hot. I'm trying to avoid a manuel isolation switch that can be forgotten.

You need either a battery isolator or a relay to charge it only when the key is on.

Yeah get a starter relay and tie it into the key on thing.

Yeah get a starter relay and tie it into the key on thing.

Is the "key on thing" listed in the owner's manual?

Sounds like someone calling computer tech support and saying the "blinky thing isn't on the TV thing". ):h

Yeah get a starter relay and tie it into the key on thing.

problemchild, I'm glad you showed your sisters !!!!!

JoBadluck,

Here are their cousins!