Hi all, I recently bought a 2001 F150 SuperCrew with the 4.6 with approximately 250k miles. My battery kept dying (brand new battery, the one that was in it was kaput) and I couldn't figure out why. I took the alternator out and had it tested by my buddy at AutoZone, but it tested good. Anyway my suspicion is that something is draining the battery while the truck is off. I recently discovered that the air sometimes stays on when I kill the engine. Occasionally, I hear a relay clicking under the hood when the truck is off. Any idea what could be causing this? I admit I don't know much about the electrical aspect of these thinga. Also, I don't know if this is related, but my factory stereo sometimes has no power. Any advice/suggestions would be greatly appreciated. Thanks all

 

All are common symptoms of what I call "Leaky Windshield Syndrome".

Water drips down into the GEM module and the fuse box under the dash and causes random mischief.

 

Alternators can test good on the bench and still fail in the vehicle. On the bench since during the test it is not exposed to the heat, cold, wind, moisture, etc. like what happens in the real world.

By "air" staying on do you mean the blower motor? If that's the case the blower motor is a significant draw and will drain the battery. The clicking relay could be the high speed blower relay if you're hearing it only when the blower turns on.