[Early_S_Man]

John T,

You are very fortunate to have a Fluke 88 ... a model they shouldn't have discontinued!

Your system seems to be suffering a bit from old age, not any failures, per se ...

The blue wire does seem to me to have too much resistance in it, which is causing the dimly lit warning lamp above 2000 rpms. Try cleaning all of the connections from alternator brush holder to warning lamp bulb holder with Q-tips dipped in vinegar, followed by a rinse with distilled water, blow dry, and final rinse/brush with fine, soft toothbrush [particularly at the two 14-pin connectors, which have silver-plated connector terminals -- clean female receptacle with pipe cleaner, male terminal with toothbrush] and 91% isopropyl alcohol. After the circuit is performing normally again, all connections should have a coating of Dow Corning 4 or 111 applied to protect from moisture and oxygen ingress for the next 20 years!

After cleaning, all of the female Faston connectors should be re-tensioned on both sides with needle-nose pliers -- just slightly, not enough to close the gap to zero! With clean, tight connections along the blue wire, I don't think there should be more than 0.4 Ohms in the D+/61 lead end-to-end from brush holder to bulb holder, ald the Voltage drop should be significantly less than 1.0 Volt, say 0.3 - 0.4 Volts, maximum.

Your Voltage regulator is not failing, just a bit out of adjustment due to wear on the 'points' [contacts] ... and being a mechanical relay-style regulator means it can be adjusted, after the 'points' are cleaned and burnished. At 4000 rpm it should not put out more than 14.5 Volts at the battery terminals.

One final comment ... alternator measurements and adjustments should be made with engine fully warmed-up, as Voltage output tends to drop measureably when engine is hot at running temp.