GM Alternator Identification
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This process is pretty easy using the visual chart shown below. This chart is taken from the American Autowire catalog - thank them for the nice graphics. They do have a couple of errors though - like what alternator got used in 1985? (I believe it was the "SI" style.) Also, the externally regulated units were not used past 1972 in many cases - I know because I have a 1973 Buick and all of the manuals for it - and it's definitely the "SI" series internally regulated alternator. :-) Also, I believe that the internally regulatred alternator was introduced in some vehicles as early as 1969 and thus there was overlap between what alternators were used when. I'm going to trust that the info for the newer CS series alternators is accurate since I know very little about them and don't own any vehicles that new, but again, I would expect some overlap in the year used as a new style was introduced and the old style was phased out.

Be aware that the most commonly used SI series alternators can be found in three different basic types - 10SI, 12SI, and some rare larger-case designs known as the 15SI and 27SI series. There is a great page detailing the differences on the MAD Enterprises website that you should take a look at.

You will notice that there are small wiring schematics on the picture below - they give you some helpful hints about identifying these things - the plugs on the alternator are unique to each series of alternator as is the wiring needed to make it work. Also notice that the "SI" model wiring shows the classic trick of wiring the #2 wire on the connector directly back to the BAT terminal on the alternator - you'll lose the remote voltage sensing feature, but it will work in a pinch.


Generators are not covered here because I'm not sure they were standardized very well. Typically they are smaller around than the 1963-1985 alternators (about 70%-80% of the diameter of the alternators) and they are much longer (measured from the front pulley to the back of the unit) - about 12 inches as opposed to about 6 inches for the 1963-1985 alternators. Once you've seen one, it's pretty obvious what they look like. It's definitely not like any alternator I've ever seen and I think they're pretty hard to get confused. Below is a picture comparing a typical GM externally regulated alternator to the generator from my 1958 Buick.


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Page last updated 01/02/2009 01:51:39 PM