Got a 2004 F150 with a pretty excessive drain on the battery that I haven't been able to run down yet. Tried pulling every fuse, disconnected the alt, lights, etc etc. When the problem first started, I heard a rapid click that sounded like it was between the cab and the bed, and went on even with the keys out. Now the battery drains in just a day or even overnight if I leave it connected.

Found this wire along the driver's side and there's a cut wire here. Can't figure out what this is supposed to be or if this could be a problem. Can anyone ID it for me? Thanks!

 

That vampire tap is something aftermarket, trace the green wire and see where it goes.

As for the clicking sound that was coming from the BCM/vsm (goes by different names depending whom you ask) on the back wall of the cab.

And from my experience that BCM relay clicking noise is a symptom of the battery being almost dead, but it's not necessarily what caused it to go dead.
Try pulling the fuse for the radio, that seems to be one of the common drains on these trucks for some reason.

 

I pulled the radio out and disconnected it - no change. I'll trace that store and see what it is. To be continued.

 

when you tested (for drain) after pulling the stereo out, did you make sure that keep alive power had shut down?

 

Ok for that matter the red wire is also something aftermarket now that I look closer, so follow it too. Anything factory would have been inside a wire loom.

If you want to eliminate the BCM for drain testing you could remove the back of or the rear seat and unplug it, but some functions like remote entry will not work while it's unplugged.

 

That red wire runs all the way to the positive battery cable, and then runs along the bottom and disappears up between the cab and bed.

 

All good info given by others.

Also, when testing for battery drainage, did you use the DC amps scale on a multimeter,, and connect it in series between the negative battery terminal and cable? Asking because pulling each fuse with that hookup should have shown the faulty circuit.

Also, if you have a regular cab the BCM/VSM is on the left B pillar. If not, considering my difficulty in removing the back of the rear seat, I would check the draw after pulling each of the fuses for the BCM/VSM, starting with fuse 6, to confirm that the draw is coming from there before removing the seat.

 

Have you disconnected it from battery yet?
was it fused?

 

I had a problem where my battery would go dead when I let my truck (05 F150) sit for 4 days & I read about the radio problems. I unhooked it & let the truck sit for 4 days & no more problems. I replaced the factory radio with a JVC I got from Crutchfield & it has been fine ever since. I would pull the radio & unhook every wire & see if your problem goes away.