The alternator was getting hot with the engine shut off (eventually ran the battery down to zero). Since I suspected it was causing an annoying squeak anyway, I bought and installed a new alternator. Imagine my surprise when after I hooked it up I noticed it starting to get hot just like the old one (engine off). After I disconnected the battery, I checked a few of the wires with a multi-meter. I discovered that the heavy black/red wire bolted to the alternator was showing a full ground (even after disconnecting it from the unit). I also noticed that I would only get a partial ground if I disconnected the 3-prong plug from the alternator.
Mostly just to see what would happen, I reconnected everything and fired the truck up. It sounded great and there were no indications of a problem from the vast array of idiot lights (or light). However, when I touched the casing of the alternator after 30 seconds of running, I almost left some skin behind it was so hot. I immediatly shut it down and disconnected and removed the battery. I'm starting to suspect that I just replaced an old bad alternator with a new bad alternator.
Any thoughts?