- from time to time the alternator output drops to 9v. Sometimes cleaning the regulator contacts fixes the problem. This time it didn't so I tried a known good regulator from another car and it didn't work either but was fine when I put it back it it's original car so I replaced the alternator/regulator with a rebuilt unit... same problem. Then after watching it idle for a while the alternator voltage went back to 13+v at the alternator terminals but was still reading 11+v at the battery. I was thinking ground so I made a good ground connection but no change. Today I have 11+ at the alternator and at the battery. Any ideas?

 

Sounds like either an internal alternator problem, like a shorting wire, or you have intermittent high resistance in the circuit from alternator to battery. Where are you measuring voltage at, alternator terminals?

Regards, Andrew.