I have a 1972 Series III. The front headlights lights are dimming and the horn is not working. Neither has been a problem in the past. I put a volt meter on the battery (engine off) after charging it overnight - read 12.4 volts. Turned on the engine and throttled her up a bit. Put volt meter on the battery while running and it read 12.2 (should be 13 to 14 with motor running). Alternator is only 3,000 miles old (see picture). Belt looks great and taut. Spinning like a top with the engine on and not making any funny noises.

What is the best way to "test" the efficacy of the alternator? Advice requested. Other suggestions welcome too. Thanks in advance.

I will note that the horn and headlights seem to be on the same circuit. I would deduce that is the problem if it were not for the fact that the battery is reading 12.2 volts with the engine running

Name:  Alternator.jpg
Views: 992
Size:  54.6 KB