06 5.9L Auto Dead Battery ??

[cbmkr]

Tried our second truck this morning and the battery was dead , this has happened in the past and only does it when it is cold. Truck is 2006 2 wheel drive 4 door 5. 9L auto with 22K miles. We are trying to figure out what is drawing this down as it will only do it during cold weather. This truck is stored inside an unheated garage. If you unhook the batteries you are fine but leave them hooked up its dead ,NO dome Light even and it doesn't take weeks just a couple of days.

Any ideas ???

 

[InfernoB]

I want to say the fuel heater is going on, but I'm not certain if it does with the key off?

Unplug the wire going into the heater thermostat and see if it starts after several days if you don't use it.

 

[cbmkr]

It is narrowed down to the power box were the fuses are ,there is a good draw from it with everything off. I am thinking there is a relay that is closing when temp goes down.