The 2525 has an electronic tachometer. It appears to get its signal from the 4th brown wire from the alternator. My troubles were oriented around the alternator field brushes, and a loose circuit at the fuse. Once I centered the brushes on the field collector rings, and corrected the loose wiring at the fuse, The amp gage truly showed that the alternator was putting out, and the tachometer became rock solid again.
I wonder how hard it would be to switch over to that type of tach. This mechanical one just doesn't seem to want to work very well no matter what I do.