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  1. #1

    Default Dual Batteries (Aux) GMT900 2500HD Crew Cab 6.0L

    Okay, so I've been following multiple threads for awhile on aux battery installation and I'm lost now, expecially looking under the hood and now have some questions. Is my truck already setup for dual batteries? It seems all I am missing are the positive and negative cables for the aux battery on the driver's side.

    There is a red wire running from the battery to a fusible link on the firewall, which in turn runs along the entire firewall into the big black electrical panel on the drivers side.

    Also notable are two sets of coiled red wired, one is taped to the wiring harness below the master cylinder and another is coiled up and tucked along the side of the electrical panel.

    Here are my findings: Please note, I have no clue what the coiled red wires are for; thus me asking the experts here.

    Red wire coiled up under master cylinder to wiring harness:

    Fusible Link with battery cabling running along firewall to electrical panel on driver's side:

    Dual battery cables one to the starter (guessing) and one to the fusible link:

    Empty battery tray, driver's side behind headlight:

    If you look closely, you can see the coiled red wired below the master cylinder and the other on the right side of the black box.

    Coiled red wire along side driver's fender next to electrical panel:

    So, my question is: What do I need to get the dual battery setup installed in this 2009 GMC 2500HD 6.0L Crew Cab?

    Thanks for your help!
    Last edited by Combat_Vet; 03-02-2010 at 06:30 PM.
    2013 Chevrolet Silverado 2500HD Z71/LTZ Crew Cab Duramax 6.6L HD / Allison 1000

  2. #2
    Master Mechanic TritonBoulder47's Avatar
    Join Date
    Nov 2009
    Tunkhannock, PA (North East)


    That strange... Do all NBS trucks have the battery on the passengers side...? In my Av my stock battery is on the drivers side up by the headlight and my secondary battery goes on the passengers side back by the fire wall...

    Sorry I don't have any info for you on this. I'm not too familiar withthe NBS trucks... Good luck though!!!

    Tim a.k.a. Da' Boulder

    2003 Chevrolet Avalanche Z71 - Custom Emergency Response POV

    Firefighter, Fire Policeman, Ambulance Driver, Rescue Tech, Emergency Lighting Installer

    Tint, 20's, Bull Bar, Intake, Exhaust, Billet Grill, Stereo, Custom Console, Emergency Equipment, and the list goes on...

  3. #3

    Question Dual battery setup

    I have an '09 Silverado 5.3L LTZ w/145A alternator and the main battery is on the passenger side near the firewall. I also have the 2n battery tray on driver's side near headlight and have been investigating what's needed to install 2nd battery for motorcycle winch and aux 12VDC power outlet. I came across a SurePower 160A electronic battery isolator and was glad to see your pics of the fuse block and taped wires. I will check my truck for these same wires and see what I can find out about the intended use.
    Attached Thumbnails Attached Thumbnails IMG_1495.jpg   IMG_1489.jpg  

  4. #4
    Sr. Apprentice
    Join Date
    Nov 2009
    Grandview, WA


    The wire next to the fuse box are too small for battery terminals, it looks like 12+ power for trailer receptacle.

  5. #5
    Jr. Engineer lsutoms's Avatar
    Join Date
    Sep 2009
    baton rouge louisiana


    [QUOTE=TritonBoulder47;227957]That strange... Do all NBS trucks have the battery on the passengers side...? In my Av my stock battery is on the drivers side up by the headlight and my secondary battery goes on the passengers side back by the fire wall...

    yes all NBS trucks have the main battery on the passenger side by the firewall and the spot where the battery is in the OBS trucks is empty as shown.. thats where my train horns are!!! =]
    "I'll Sleep When I Die"

    2009 Chevy Silverado LT1
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    galls street thunder deluxe siren/PA

  6. #6

    Default Fuse block terminal

    It appears that the larger of the terminals is a straight shot to the main input blade/post.
    The question is can you hook to it for a dual battery or is it just a supply for other accessories?

  7. #7


    I know this dual (auxiliary) battery thing has been beat up for a long time on multiple forums with varied information on how to get the job done. The good news is that I have been working with the new owners of Wrangler Power ( to develop a complete kit for NBS GMT900 2500/3500HD trucks.

    My duty vehicle is a 2009 Tahoe Police PPV with factory dual batteries and will be taking measurements and photos along with the GMC Sierra for them to develop a complete kit, which will be safe, reliable, cost effective and appear like an OEM kit.

    So, for now a complete kit is in R&D! If there is any interest in them putting this into their catalog after I guinea pig the kit, let me know.


  8. #8


    The auxiliary battery thing has, indeed, been beat up on multiple forums with varied information -- because there's more than one correct way to skin this particular cat and one's approach depends a lot on one's needs AND one's budget.

    Some people need 24v and wiring in series. Some need 12v and single battery isolation (a la single rectifier). Some need 12v and dual battery isolation (a la dual rectifier). Some are ok with voltage drop induced by diodes while others can tolerate no voltage drop and will pay heavily for mosfets. And then there's solenoids somewhere inbetween...

    I like the idea of a complete kit ... but I'm hoping it's not positioned as the lone proper solution because there isn't such a thing. The solution one needs ... depends on one's needs.
    Last edited by SurrealOne; 09-24-2011 at 02:36 PM.

  9. #9
    Sr. Apprentice
    Join Date
    Jan 2010
    Old Bridge NJ


    Combat_Vet, I too an interested in a dual battery setup for my '09 2500HD. How is the R&D coming?

  10. #10
    Master Mechanic zigger215's Avatar
    Join Date
    Sep 2011
    Fairbanks, Alaska


    Wiring DC in series is additive (thus you would get 24v from two batteries). Wiring in parallel is canceling so you could have five batteries in parallel and still have 12v. Also an isolator is a good idea but it is possible to just wire the two batteries in parallel with each other. What an isolator will do is say for instance your aux batteries goes bad and starts to drain the starter battery, an isolator prevents this phenomenon from happening.

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