So, I'm fairly familiar with wiring up Delco alternators (10si I think?) to our older Volvos. I've also used them off small engines for a standalone battery charger.

This latter application is what I need to do again, but.. there is an extra spade pin on the new alternator I got. See picture, top is a Delco from a Volvo 1800e, bottom is the new one that I want to charge our battery bank with.

Joker in the deck: This new one is 24v, rather than the usual 12. The pigtail from the 12v guy fits the normal 1 and 2 plugs on the alternator.

Any clue what that third pin is, and how it gets hooked up? In case the image doesn't show up, it's at http://i.imgur.com/DO0VAWG.jpg
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-Matt I ♥ my ♂

http://www.delcoremy.com/getattachment/Alternator-Models/24SI-Heavy-Duty-Alternator/24SI-28SI-Installation-Instructions-10524210.pdf.aspx

should help
pretty sure the third wire will be rpm tach signal.....mechanical diesels need an rpm source and often use the alt for this....the fact that yours is 24volt indicates possible truck (diesel) application

Ah!!! Yes. Excellent thought, even though I'm not working with a 24-SI, that totally makes sense. And yes, the equipment list for this alternator includes and extensive lot of heavy equipment type stuff.. backhoes, loaders, forklifts... etc.

Thanks! I bet you're right.
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-Matt I ♥ my ♂

Matt;

Patrick's answer may be the ticket, but if you can also locate and post an internal wiring diagram, I can maybe confirm third connection is an RPM output.

Cheers

Thanks for the reply, Ron.. I cross posted my question to a vintage machinery site after posting here, and got back a confirmation that the third post is an A/C out, indeed, most likely used for a tach. And that it can just be disregarded for my application.












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-Matt I ♥ my ♂