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Discussion Starter · #1 ·
Ok so my "gen" light has been on in my truck for about the past week. I haven't had tine to deal with it till today. And it finally got to where my truck barely started. So I cleaned all the terminals on the batteries and the ground wires from the battery and alternator. So i'm wondering...if it is a bad alternator or a bad voltage regulator? I believe is what I've heard. I can't hear the alternator kick in. such as when I start the truck normally you can here it kick on. Then kick off. I can't hear that. So what do you guys recommend or think

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VP of the dry side
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Discussion Starter · #2 ·
Tested the batteries with the truck of and they were 12.26. Then started the truck and they read 12.18. And tested the alternator and it was the same voltage as the batteries so i'm lost here. is that the alternator going bad then

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First I would charge the batteries. Once that was done I would go to a local parts store or alternator and starter rebuilder that has a tester. Then take the alternator off and see if it tests good or not. If the alternator tests bad you need to get it rebuilt. If it tests good either you have something like corrosion on the terminals or connectors, burned nuts, or a bad voltage regulator which is in the PCM.

Probably your brushes need to be replaced in the alternator but there is no way to know from here.

Testing is the right way to tell. Guessing is just guessing.

All your test showed is you are not charging and used some power when starting. You still have the question of alternator or regulator until you test and rule one out.
 

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VP of the dry side
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Discussion Starter · #4 ·
Can I test it on the truck or do I have to take it off

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I have always seen bench testers.

That requires taking the alternator off the vehicle. That really is a quick and simple job as long as the bolt is not frozen in the threads.
 

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It is very simple to test! There are three wires going to the alternator. 1 power should have 12v at all times, when charging will read 14V. Then you have 2 ground wires, they should be much smaller gauge and going to the internal reg. 1 is a constant ground the other is the regulated ground from the pcm. You can then ground apply a ground and see if the truck starts to charge. If it does you either have a bad pcm or the crank sensor is bad. Does the tach work when its running? If not thats the problem right there. Crank sensor or pcm. Hope I helped
 

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Discussion Starter · #7 ·
Yep the gauge works

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