If it's a substantial drain, remove the negative Bat terminal & read voltage between Neg Bat post & terminal connector. While you're monitoring that, have someone else pull fuses one at a time. When you pull the fuse w/ the draw, the voltage reading will drop. This will at least isolate the circuit involved.
Other possibilities is a connector that appears clean & secure, but is not, or a cable that is compromised by corrosion hidden under the insulate sheathing.
"Saving the World....One Ford Truck at a Time."
Last edited by ymeski56; 01-18-2013 at 11:42 AM.