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Amedee
Amedee, Pontiac Technician
Category: Pontiac
Satisfied Customers: 24786
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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pontiac G8 GT: new high output alternator direct bolt on pontiac

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new high output alternator direct bolt on pontiac g8 gt old 140amp new 180amp new alternator not turning on checked connection still not turning on what could be the main problem thanks.
Hello and welcome to Just Answer!

My name is XXXXX XXXXX I can assist you with your question.

Are you saying that the alternator is not charging after it has been replaced?

Is the check engine light on? Are there any codes in the computer?
Customer: replied 3 years ago.

the alternator light comes on after engine has been runing few second.

Mike,

Thank you for that information.

Have you checked the inputs going into the back of the alternator?

Are there any codes stored in the computer?
Customer: replied 3 years ago.

The check engine light is not on just the alternator light.

Mike,

This charging system uses a pulse width modulated 5 volt circuit to command the regulator to charge the system at specific voltages. I would start by checking for power on the BIG RED wire going into the back of the alternator. This wire should have full battery voltage on it at all times. If this checks out ok, then check the two wires between the ECM and alternator. If all checks out ok, either the new alternator is bad or the ECM is at fault.

Another good way to check this circuit is to able to apply voltage to the "L" terminals of the regulator and the alternator should charge. If so, then I would suspect a bad ECM or a wiring issue between the ECM and alternator. If not, then I would suspect a bad new alternator.

Here is a wiring diagram of this circuit.

graphic

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