How to Identify GM Alternators

Written by floyd drake iii
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How to Identify GM Alternators
Same model Delco-Remy alternators may have different AC Delco part numbers. (Hemera Technologies/ Images)

Alternators provide electricity to a vehicle while the engine is running, charging the battery in the process, and when the engine is turned off, the alternator alternates the power supply to the battery. General Motors exclusively uses alternators manufactured by Delco-Remy, and since Delco-Remy alternators are an industry standard, many copies exist, especially on engines where the original alternator has been replaced. Proper identification of common Delco-Remy alternator models, such as the 10SI, 12SI, 15SI and 19SI, eliminates the possibility of imitations, many of which are inferior to genuine Delco-Remy alternators.

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  1. 1

    Examine the Delco-Remy alternator. The alternator is located at the front of the engine, usually toward the passenger's side of the block. Look for a fan with a pulley on the front, with a belt attached to the alternator and the main pulley at the front of the engine. On the back of the alternator housing, "Delco-Remy, Made in U.S.A" is cast in raised letters in a prominent location.

  2. 2

    Locate the Delco-Remy identification tag or sticker. At the factory, Delco-Remy places an identification tag on the alternator housing. This tag contains the Delco-Remy model number, the AC Delco part number and alternator specifics, such as voltage and amperage. The ID tag contains the necessary information for proper identification of the Delco-Remy alternator.

  3. 3

    Identify the differences between Delco-Remy and GM alternators. Differences between alternators with the same model number exist, mostly concerning the amount of power, or amperage, the alternator produces. Vehicles with many electrical devices and options require an alternator with a larger amperage rating. The amperage rating is found on the ID tag, and can be referenced by using the AC Delco part number. For example, the Delco part number "321-39" identifies a model 10SI with a 63 amp rating. Always use the AC Delco part number when referencing the alternator, or dealing with a parts or service department.

Tips and warnings

  • Delco-Remy alternators always have the air intake vents on the back of the alternator. Copies usually locate the vents on the side of the alternator housing.

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