Update, I pulled the alternator out again (by the way, is there a way to get it out without taking off the radiator hose and spilling some anitfreeze) and checked the three-pin plug, blew it out with an air compressor, reconnected, and confirmed the positive voltage connection was nice and tight. I also trace the signal wire to another plug and cleaned that one. All this had no effect. But, I was able to take it on a four hour drive with no problems at all--voltage stayed between 13.8 and 14.2 with brights on. The warning still comes on every time I start the engine though. I'm going to have to check all the fuses and connections other than right at the alternator.