Very usefull for finding problems with internally regulated alternaters. But what about externally regulated?
Although newer internally regulated alternaters usually fail completely when they go, in the case of a partial failure, or to rule out the alternater as an issue this test is perfect.
Some of us are using alternators on our early Ford tractors.
The Chevy unit is usually the cheapest. My auto electric shop will provide an unregulated alternator for much less $$ than the store bought one. They even have large frame units. The only real job is installing on the engine.
Michael
First time I've seen the "voltage drop accross a connection" in sailing circles. We used this technique to find faults when I was an auto mechanic all the time. A great way to tell which battery terminal is not doing its' fair share.