I normally hang out over on the 7.3 board but my brother-in-law has an 03 6.0. It is running the battery down as soon as you hook the batteries up. Anybody had any experience with this?

 

Park in a place where is will stay dry. Put the batteries in and open the
hood and drivers door. Let it sit for about 45 minutes. The with a clamp
on amp meter on the main cable from the driver side battery check what
the draw is. Then unhook the passenger side battery. Now the fun starts.
Unhook the lead going up to the alternator and check it again. Make notes
each time. Get a list of what fuse does what before you start. Now you go
to the in cab fuse box and start removing the fuses. don't pull the one for the GEM
until later. Your looking for the one that drops the draw down quite a bit.

The reason for the 45 minute wait was so all the systems can time out and go to sleep.
That is why I had you open the door. If you open or close any door the cycle will restart.
The sane goes for the hood if you have a light even if it's not working it can wake
the GEM back up.I am not sure if putting a fuse back in will wake it so mark them and
put then mack when your done. If you get down to the GEM and are still seeing the heavy
draw we can try and tackle that after you have this part done.

A sensitive clamp on amp meter makes this easy. The type you have to
break the line is harder but will work too. You will need a resolution in the mA range.
Post back what you find.

Sean