I copied this from my other post today;
I am a master electrician. I have worked in a custom Electric Vehicle shop doing R&D and have a mini farm with plenty of equipment to give me problems. Some may think it's excessive that i clean and apply electrical grease to
battery connections and grounds on an annual schedule. The weather in my region is zone 7 and salty fog being coastal with mild winters. Everything is wet from September to May. Anything unprotected corrodes. My shop friends are the following spray cans on a shelf like little soldiers ready for war. LPS, Fluid Film, T9 boeshield, Silicone spray, white lithium, oxide electrical grease ect. All my equipment has high current flexible ground straps bonded to the starter cases, the chassis, and the back of the alternators back to the
battery negative. This makes sure the engine critical components are at a negative potential and not being used as a path for current to flow. For this I get starters that engage, alternators that charge and no electrolysis destroying the engine metals. I look at it all like Its a marine environment.
Poorly grounded alternators or poor connections to the alternator can cause the internal voltage regulator to be unstable. Looks like some kids playing with a dimmer switch on your headlights causing them to go from dim to bright kind of oscillation. That said I have found that when all connections to the alternator are %100 some still do it. I took those alternators out to closer examine on my bench. This is what I discovered. The pot metal case the alternator is housed in was corroded and not providing a good connection to the internal regulator electronics that are bonded to ground via the alternator pot metal housing. So a bad connection internally cause the regulator to be constantly adjusting the field current. Solution was to glass bead or clean and lube the inside of the alternator housing and reassemble. My shop records show two instances of a pooched regulator as well. The 10si and 12si regulators usually work or not. Not much in between. Other alternators can have a bad (hunting) regulator that still charges even know the voltage is like a yo-yo
