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Old March 23rd, 2021, 06:10 AM
biscaynebirdie biscaynebirdie is offline
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Join Date: Jan 2021
Location: Santa Rosa, California
Truck: 1965 1000 Series with 250 engine and SM420 transmission
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Unhappy Overcharging alternator and buzzing voltage regulator

I keep blowing out flasher relays, oil pressure switches, and heater blower fuses in my truck, so I decided to check the voltage at the battery when at idle: 15-15.3 volts. The 1963 Chevrolet Truck Shop Manual says that 15 volts is the maximum voltage that should be had (generally, as I’m sure you all know, 12-14 is what is generally acceptable), so I have a feeling that this is probably why I keep ruining these various electrical components. I assumed it was time to purchase a new voltage regulator.

I drove down to O’Reilly and picked up a brand new regulator (made sure it was made in the USA) and decided to give it a try. With the key turned on, the generator light lit up as it should and went out when the engine started up. However, when I bumped up the RPMs just a little bit, the generator light turned on and a buzzing was heard coming from the voltage regulator. I checked the voltage while this was happening, and it was reading an astounding 16-17 volts and climbing! Not good... When I increased the RPMs a little bit more, the generator light turned off and the buzzing stopped (voltage returned to 15-15.3 volts). As I released the throttle, it buzzed again (generator light lit up as well) then stopped buzzing when at idle. I popped the cover off of the voltage regulator to check if I could see what was causing the buzz. It was, as I had assumed, the set of points that generally will be open before the engine starts and will close once running. I’ve included a picture of said points below (it’s circled in red, for ease of viewing).

I checked for good continuity in all wires in the area (voltage regulator, alternator, horn relay), as well as cleaned up all of the connectors (adding some good old dielectric grease, too). I made sure that the red wire that goes from the battery to the regulator was getting a full 12 volts, as well as checked for 12 volts on the brown wire with the key on and no volts with the key turned off. Hmm...

I’ve read that one possible culprit could be a bad diode in the alternator. Another culprit could be that my battery is at the end of its life. However, I’m not so sure about the latter since with the engine not running, the battery sends out a good 12.7-13.2 volts.

So... any ideas?
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