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showbizkid
03-18-2019, 04:43 PM
My next-door neighbor (a kid with not a lot of mechanical experience) has a '64 Chevy C10 pickup with a transplanted engine - a '72 350, from what I can gather. Yesterday he came down scratching his head, saying his 30-day-old battery had died, so I went up to look.

The truck has a GM 10SI-style 3-wire alternator from NAPA that he installed after some charging problems a few months back. Part # 213-4011 appears to be internally regulated - but the truck also has an old-style fender-mounted voltage regulator. The wires are all spliced so I have no idea what's connected to which terminal. Following, photos of each.

Neighbor fired up the truck and revved to 500 RPM, and I measured voltage off the battery cables at 12.23 volts. I then measured voltage from the alternator BAT connection at 12.23 volts as well - 1 - 2 volts too low.

As I am no expert in GM systems, I have no idea what to check next. Is the alternator not performing properly, or is it over-regulated? Or is that all the voltage a brand-new battery fully charge battery should be receiving?Any advice is much appreciated.

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Dick Steinkamp
03-18-2019, 05:05 PM
Electricity is pretty much magic to me, but I guess I'd start by wiring it correctly and eliminating the old VR...

http://vivresaville.com/wp-content/uploads/3-wire-gm-alternator-wiring-free-wiring-diagrams-of-chevy-3-wire-alternator-diagram.jpg

It could be he has already fried the new alternator. He can remove it and take it to one of the auto parts stores that can test it for him.

showbizkid
03-18-2019, 09:01 PM
Thanks, Dick. Agree that there needs to be a wiring change - two regulators is just not right.

IIRC, if you run the engine and remove the two socketed leads to the alternator, you can short the lugs and force the unit to max output, right? Isn't this a way to test whether it's operating correctly?