I've been having electrical problems that I thought were caused by a short in the a/c wiring. Now that it's cooled off I kind of put it on the back burner. When I'm driving around the ammeter is right in the middle if I've got nothing electrical turned on. Last night I drove home in the dark 30 miles from a fishing trip, and noticed that the meter went from half way between left and center to gradually almost all the way to the left. As I neared home the radio would fade in and out in when the turn signal was operating. I stopped to get something to eat on the way home and when I went to start the engine it wouldn't turn over. Got a jump to get home, but when I got back and checked the battery it tested "good", just as it did when I started out. What gives? All connections to the battery and starter are tight and the wires are in good condition. Somebody told me that some auto parts stores can test the alternator without taking it out of the vehicle. Is this true?