I bought my 68 pretty much assembled, including a chrome alternator with unknown output. I am about to install some larger cooling fans and would like to know how to verify the alternator output. I have checked it for numbers and can't find anything. Is there a way I could check it or do I need to pull it and have a shop check it?
Thanks

What type of alternator, externally or internally regulated, 10si, 12si, CS130 or? To tell the difference between externally or internally regulated go here (http://www.chevelles.com/forums/showthread.php?t=105661) To tell between a 10 and 12si go here (http://www.madelectrical.com/electricaltech/delcoremy.shtml)

You could full field it through an ammeter to get a good idea as to output amps. A paper clip in the male voltage regulator plug from "F" to "3" will give you full field current for maximum alt output. This assumes that you have an external VR still.

Test at around 1800 RPM. Test only for as long as it takes to determine amps.

Typical GM alts, back in the day, were 37amp, 42amp, 55amp, 61amp, and 63amp ratings.


If you have a 10SI there is a "D" shaped hole on the back of the alternator. You can insert a screw driver through that "D" shaped hole and touch the metal tab inside the hole while simultaneously grounding the screw driver against the "D" hole edge.

That will full field a 10SI.

How you do that with a CS130 I have no idea. Sorry.


Looking at the stuff Elree posted the 12SI is full fielded in the same way as the 10SI. You can also clearly see the "D" shaped hole that I referred to on the back of both the 10SI and 12SI.

Same deal here, have an ammeter hooked in series with the + battery and you'll be able to see alt output.

It looks like it’s the 10si, internally regulated. Its aftermarket; chrome with hardly any markings.