Question about Pontiac Grand Am
GM alternators are internally regulated. There aren't any relays or external controls for the alternator in this car. The alternator in this car only has 3 wires connected to it. The first wire is the output wire, and it is connected directly to the battery. Strictly speaking, the car should charge the battery with only this one wire connected. (GM alternators are sometimes called one-wire alternators because you only need to hook up one wire for them to work). The other two wires are for diagnostic purposes. The engine computer uses signals from those wires to know when to illuminate the battery light in the instrument panel.
You could have a problem with the output wire. I would check that first. There is a stud sticking out of the alternator on the side opposite the pulley. A connector on the output wire goes onto this stud and is held in place with a nut and locking washer. This wire probably runs to the starter solenoid, but it could also run directly to the battery positive terminal. Just make sure to disconnect the negative battery terminal before you try to test this wire (to avoid shorting the battery + and - terminals together). Clean the connectors with a stiff wire brush and put some silicone grease on them to prevent corrosion. If you have a multimeter, you can check for continuity through the wire, but this may not find all faults (because a multimeter only puts a tiny bit of current through the wire to test for continuity, but the alternator puts ~100 amps through the wire.)
One bad thing about GM alternators is that they are generally not very reliable. If the wire checks out, I would suggest you have it tested. Most auto parts stores have equipment for this purpose. Even though you have replaced it 3 times, it may be bad. Just be sure to buy one with a lifetime warranty (and keep the receipt) because chances are that you'll need another one some time soon. (For what it's worth, my car is on its 4th alternator.)
Posted on Jul 28, 2009
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Posted on Jan 02, 2017
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