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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: GM
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a 2006 3500 chevy 6.6... my question is were do the 2

Customer Question

Hello I have a 2006 3500 chevy 6.6... my question is were do the 2 Alternator Wires run to. They are the dark brown and tan wire I am getting no juice to either wire with the key on or truck running. And I have checked all fues I can find
Submitted: 1 year ago.
Category: GM
Customer: replied 1 year ago.
I have cleaned all connected ends.. alt is not charging my batteries I put new alt on my truck still not charging my truck all fuses are good that I can find. The 2 top wires coming out of alt does not have any power going to them were do they go.. I have 1/2 the wireing harness taken apart wires are not broken any were.
Expert:  Juan Crespo replied 1 year ago.

Are just trying to find out where those two wires go, or why the alternator(s) are not charging? What VIN, 2 or D? one or two generators?

Customer: replied 1 year ago.
D one generator
Expert:  Juan Crespo replied 1 year ago.

I'm sorry... and what is it that you're trying to find out?

Customer: replied 1 year ago.
My alt is not charging.. the 2 wires come out of the pulg of the alt has no power with truck off or with truck running... were do the wires run to
Expert:  Juan Crespo replied 1 year ago.

I apologize. I should have read your post more carefully.

Those two wires go to the diesel ECM which controls charging. Do you have a scan tool capable of reading engine data?

Customer: replied 1 year ago.
No sir no tool. I have a programmer that can read codes on the truck
Expert:  Juan Crespo replied 1 year ago.

OK. So far we know the charging system is not working. What we need to do now is find out why, is it a bad generator not putting out enough of a charge, bad batteries unable to hold a charge, or a bad control module not "telling" the generator to do its thing?

Let's start with the fact that at 12.2 volts (equal to about 60 %), your batteries need a charge. Fully charged those puppies should read 12.6 volts across. Most of all, trying to charge the batteries with the generator might burn it up - it wasn't made to do that.

So, first, we need to charge the batteries. Once that's done we'd be left with either the gen or the ECM as the possible culprits.

The ECM sends a duty-cycle signal to the gen field through the Gray or Tan wire. So, all we have to do is look for that signal to be present at the gen - duty-cycle means it is a digital signal that is switched on and off by the ECM, the bigger the % of duty, the more the gen wil charge.

To check it, you will need either a scope or a voltmeter capable of reading frequency (Hertz), or you can rig a Noid light like the ones used for testing injector pulse. All you have to do is touch the Gray or Tan wire terminal at the gen with the positive (Red) probe of a scope or frequency-capable voltmeter, or one of the jumpers from the rigged Noid light using it as a you would a test light (regular low-impedance test light might not work and instead cause internal ECM damage)

Please let me know what you find and/or if you have any other questions.