2016 Sierra 3500 Main and Aux batteries -

[Snowcamo]

Right on. Seems like it shouldnt be that hard to find parts.

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[Snowcamo]

I went to dealer lots and looked at trucks that had snow plow packages and  told them I was working on a project and could I look under the hood and got some # that way and the it all started to fall into place.

Do you mind posting some pics of the parts under the hood for reference?

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[Gmman]

I have two right now, I'll get more when I go outside later. The plug circled in yellow, Half of that is on the firewall by the battery. The part # on the tag is for the wire harness that goes between the two batteries. #84276395.

[Gmman]

I found this online. I didn't make the red marks. #10 comes with the harness.

[Snowcamo]

Hey thanks for all your help!

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[Gmman]

No problem. If you have a 1500 it may be different.

[Snowcamo]

No problem. If you have a 1500 it may be different.

Might just be different. Im not seeing a connector on the fire wall. Here's the tray I was talking about.

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[Gmman]

6 hours ago, Snowcamo said:

Might just be different. Im not seeing a connector on the fire wall. Here's the tray I was talking about.

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Mine looked like that also. Those battery try pics I posted should  be the same for the 1500.

[Gmman]

[Gmman]

[Snowcamo]

That's awesome! Thanks for taking time to post this up.

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[Gmman]

I looked up the battery harness for a 1500 and got this # 84276396. Rockauto has them.

[Snowcamo]

I need to search for that connector at the firewall. Hopefully I have it somewhere

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[Gmman]

It should be near where the A/C comes through the fire wall . The plug has a cap on it to protect it from the weather.

Edited December 1, 2019 by Gmman

[johnsnowkornar]

On 11/28/2019 at 10:20 PM, rebrecs said:

I have 3500 Diesel 6.6 Denali.

There is a battery charging management system built-in from GMC. Based on information in the Owners Manual under the "Battery Gauge" section, there is functionality sounding like what you would expect from a DC-DC Charger w/ Controller. However, the information only discusses the Main battery. There is no mention of how charging is handled for the aux battery anywhere in the Owners Documents. Including the Dura-Max Supplement. There is no charging controller listed on any parts breakdowns either. At this moment I am working from the assumption that either the logic is in the ECM, or the Aux Battery is a well guarded secret.

The cranking diesel battery does have a large plastic box affixed to the top of the battery with a lot of high current wiring coming in and out of it. If there is a charging controller, that would be the place for it, and it would look about like that.

However, there is no mention of that box in any parts breakdowns either.

 

Do batteries come with big plastic boxes on top these days?

I was going to look up the AC-Delco battery model #, but the mystery box obscures the battery entirely. I can tell that changing that battery would not be a fun thing to attempt.

So far I have not been able to get that box open. I need a better flashlight.

 

What is the fuel mileage for a 6.6 Duramax diesel & how much can a 3500 Duramax tow?