My battery light came on this morning, and again after work just now. It flicked on when I started the engine and both leaving home and work; lasted until about the end of the parking lot before switching off. I zipped over to Advance after work and got a battery/alternator test, everything's tip-top, 13.9 volts, no draw with the engine off. I'm totally stumped for a cause to this.

As for clues, the only two issues I have right now are the ever-present amigos (Hoping to try the Option B fix soon if it'll quit raining for a few days) and the rear sunroof has been sticking. I'll flip the switch, no movement, toggle it back and forth a couple of times with front or rear switch, and eventually it pops loose and opens. I can't see anything jamming in there, and I lubed the arms, but like I said, no draw on the battery so I don't think that's related.

Anyone else had a sneaky battery light gremlin like this?

 

Your alternator is going bad, the voltage regulator is not working until it warms up, eventually it will not charge at all.
If you could leave the truck overnight in Advance's parking lot and then have them check the charging system first thing when you started the truck I bet it would read bad.

 

That is expensive news with a DII

 

$500 bucks at Atlantic British. If you shop around you might find it cheaper.

 

Yup, found some more affordable ones just now on ebay, but ebay is always sketchy in my experience

 

Just buy from a preferred seller, thats what I do, I'm willing to pay more to buy from someone will all good feed back.

 

Keep in mind that a lot of the cheaper ones on ebay are going to be remanufactured and not 100% new. It might be cheaper to have yours rebuilt locally than buying a new one or a remanufactured one.

 

There is someone on e-bay selling new alternators for cheap, I forget who but they are highly recommended.
Its Eagle Electrics or something like that.

 

why not go with an advanced or autozone alternator?

 

There is nothing wrong with a reman alternator, get one with a warranty from someone like Napa.