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1997 GMC Yukon - How to Identify Alternator Amperage

I recently purchased a 1997 GMC Yukon. The SUV needs a new serpentine belt; however, it appears the “proper” belt length is dependent on the alternator’s amp. It appears as if the vehicle could have come with either a 124, 105, or 140 amp alternator. Unfortunately, I am not sure how the alternator’s amp can be readily determined. It does not seem to be something one can determine from the VIN or or any equipped options, and it does seem as if one can easily determine it by visual inspection of the alternator (at least not while it is in the vehicle). I suppose one could test it with a multimeter, but I am not particularly well-educated in electricity and I presume the results could be misleading, especially if the alternator is faulty in any way.

Thanks for any advice.

You remove the old serpentine belt.

Take it to a parts store and have them measure it.

Not only can they tell you length of the belt, but also the amp of the alternator in the vehicle.


Yeah but it should be stamped right on the alternator or if you can find the build sheet glued somewhere with all the option codes (RPO), one of those codes will tell the original alternator installed. But doing as Tester said is probably easier-then write it down for next time.

Stop at any GMC dealership. They can give you a print out of everything that was put into that vehicle at the factory.