would like to run dual battery set up with oem harnesses.

marcs28 · July 14, 2015

i have 2011 sierra crew cab 6.2.

CapitalTruck · July 15, 2015

There has been a lot of write up about this. Do a search.

marcs28 · July 16, 2015

did some searching but I not satisfied with aftermarket solutions. that's why I decided post here and ask.

ChevMech · July 16, 2015

My '03 1500 had a dual battery set up. Hooking it up was rather simple. The ground went to the back of the block. The positive side went from the battery to an solenoid, then from there to the battery terminal on the starter. The solenoid was triggered when the ignition key was in the 'on' position.

intheburbs · July 16, 2015

I've done the TP2 upgrade to both my GMT900 trucks - my 08 Suburan and '09 Sierra Denali. It uses all factory GM parts, and looks and operates like the factory setup on PI Tahoes.

It's going to run you about $300-$350 in parts, not counting the cost of the second battery.

CLICK HERE

I did the Suburban first. Probably took me 3-4 hours. I did the Denali second, took two hours flat.

Here's the finished project in the Suburban - the blue conduit seemed like a good idea at the time....

marcs28 · July 17, 2015

thanks guys. I have my heading now. I'm get some part numbers from the dealer. i'll post what I get later on after I finish setup.

crankman · July 17, 2015

I did my 2011 6.2 4 years ago when I added a winch. I simply put a second battery on the right side where there was already a empty battery tray. I ran 2- 2/0 battery cables around the firewall inside black wireloom connected to the primary battery using a duel battery clamps. Done. I paralleled them, didnt do anything to factory harness and my truck never noticed the addition. I didnt need or want any switching contacts or another devices that could fail. I just wanted a beefy battery and it works good and if you look under my hood it looks factory laced in along the back. There are other ways to do what you want but this is the method I used.

intheburbs · July 18, 2015

Yup, many ways to do it. And many reasons. I did it because I wanted to ensure that no matter what, whether the truck is in my garage, or we're boondocking on BLM land out west with no humans for miles, when I stick the key in the ignition the truck starts. Can't do that by simply running two batteries in parallel. To power a winch, that works fine. But if you have a drain, or run a lot of accessory power with the ignition off, you could still end up with a dead truck. I won't.

My setup uses factory parts - so if it's good enough for use in thousands of law enforcement vehicles, it's good enough for me. And it's totally automatic/passive - I do nothing additional, and I have a fully charged and isolated starting battery 100% of the time.

And I also have enough power to run a winch.

marcs28 · July 20, 2015

same thought here I see factory equip seem to last longer than aftermarket gear. thanks

marcs28 · August 9, 2015

so far I have found this and have purchased my wiring. I'll post more info soon.

5Alive · August 12, 2015

Marcos28... you are on the right path with the parts explosion diagram. It may also help you to have a wiring diagram as well.

I don't know about the GMT900 series, but in the GMT800 series, GM offered many different wiring configurations for dual batteries, denoted by RPO codes. Code TP2 was already mentioned above. In the GMT800, the TP2 wiring configuration was generally for trailering (not Law Enforcement), in that it provided a 40 amp rated circuit to the rear trailering harness, separating that duty from the vehicle's main battery. If you choose this wiring method on a GMT800, don't forget to pull the 40 amp fuse from the main panel, and move the appropriate wire off of "Stud 1", so that the starting battery is fully divorced from the trailering power circuit. I can only imagine that the GMT900 is arranged somewhat similarly, but naturally different in the specifics.

Some of the other Dual Battery wiring configurations were represented by RPO codes such as 8Y9, 7Y9, 8B0, TQ3, TUV... perhaps a couple of others... some of which were for the Tahoe Police, such as 8Y9 or 8B0 (two different wiring strategies), others which for paralleled installations on diesels, such as TQ3 and TUV. Years ago I posted more details on the connection and operation differences that distinguish these GM dual battery wiring RPOs, but because GM-Trucks unfortunately only permits searching for just the previous year, and I made my dual battery wiring posts at least half a dozen years ago, those posts are lost I guess.

(As an aside, the 1 year search limitation of GM-Trucks is a pity. The current and new members cannot easily access the older posts made back when these vehicles were new and the information was more accessible from the dealerships and fresher in the minds of highly interested and motivated owners seeking it out. Now, those original owners have since sold their vehicles to second and third owners, who are in more need of repair and maintenance information than the original owners. But on this website, the older original posts are inaccessible using a search, which could lead to the blind leading the blind.)

Back to dual batteries.... on your parts explosion diagram, an isolation relay is indicated... GM Part # 12135194. Before you order this relay, look at your firewall. Do you actually have the threaded studs pre-welded to your firewall to mount that relay? I didn't. I had to add the threaded studs, because I was unwilling to drill blind fastener holes through the firewall, not knowing what was directly behind.

There may be other unused threaded studs on the firewall of your GMT900, but will they line up with the holes of the GM relay? Mine didn't. I had to add a plate to the firewall that matched the existing unused studs on the firewall, and onto that plate I pre-fitted studs that matched the relay mounting hole pattern. Again, I was working with a GMT800, but I would suggest that anyone look out for these types of issues prior to ordering parts, because the parts you end up actually needing could be effected by the details.

In the instance of this relay, it may help to know that the GM relay is manufactured by White Rodgers. It is a "Type 120" 12VDC normally open single pole solenoid (SPNO) that has a continuous duty rating of 100 amps and an inrush current rating of 400 amps, with a die-electric strength of 500 volts. It has silver alloy contacts, with 6 ohms intermittent resistance and 16 ohms continuous resistance. I say all this to say that you can get this solenoid directly from a White Rodgers distributor, and still have all the GM OEM electrical engineering validation that you are seeking by doing a factory wiring installation... with the added advantage of lower cost, and, more mounting options and trigger terminal configuration options, since White Rodgers constructs the same solenoid with different base plates and coil grounding methods.

Factors like whether or not you have insulation on your firewall where the relay would need to mount, or whether or not you have a wiring harness with a connector already there to use, and other practical limitations presented by your vehicle not being originally built with dual batteries, might influence your decision to order this solenoid from GM, or check out the various configurations of the same relay directly through White Rodgers.

Take the trigger terminals as an example. In the GMT800, there was a "lonely connector" dangling unused along the firewall, exactly where the GM dual battery solenoid was design to mount. There was even a picture online called "lonely connector" posted by a GMT800 owner many years ago who wanted to know what it was for. This connector is a two wire Metri Pack Sealed 150 Series connector, and is identified by GM as part number 12052641 for use with dual battery RPO code TP2. It carries ignition 3 voltage and ground. It is the trigger circuit to latch the solenoid in Run. Do you have this lonely connector dangling from a harness on your firewall? You had better, because the GM configuration of the White Rodgers relay, part number 12135194, is going to need that connector to hook up to it.

If you don't have that connector currently dangling from your harness, and you've already ordered the GM version of the relay, then you can easily get a pigtail service harness with the connector and two blunt cut splice leads by ordering ACDelco part number PT374. This is a common connector, used not only for a "Battery Isolation Switch" but also as a GM "Boost Solenoid Connector" (part number 12102747). Same thing. OR, you can order a White Rodgers solenoid that has open stud screw terminals, and use eyelets on your trigger wires.

Why would you need to add trigger wires? Because even if you have the "lonely connector", the wires from that connector may not be "connected" all the way through to where they need to go. Mine weren't. The wires on my lonely connector went from the firewall to connector C100 under the UnderHood Body Electrical Center. That's where they stopped. But per the wiring diagram, the Ignition 3 circuit needed to extend through the firewall to the MidBody Electrical Center underneath the dash in order for the circuit to be complete. This is why I suggest to you that the parts explosion diagram may not be enough, you also might need the circuit wiring diagram, depending on how your truck is configured.

I had to complete that circuit, otherwise my GM solenoid (that I did indeed order from GM, before I realized that it was a White Rodgers unit, which I didn't learn until after I received it) would not work, because it was the type of solenoid that had trigger terminal connections that corresponded with the sealed Metri Pack connector.

This post is getting long, so I'm going to cut it short here, with just a few more tips and pointers I gathered from my own factory battery wiring project.

The GM wire harnesses are expensive. Most of them are worth it, because they have FUSIBLE LINKS already built into them. The time it takes to splice fusible links into bulk battery cable, and the consideration it may take to size the fusible links correctly for the current capacity of the cable being used, and to make those splices reliable... is worth the cost to pay GM to have done all that for you.

However, there is one wire harness that isn't worth buying from GM. It is a simple 12 guage wire that goes from the additional fuse connection box to the trailer wiring post in the Underhood Electrical Center. That wire isn't worth the high cost. It has no fusible links or special terminals on the ends, just closed eyelets. I would source this wire locally, but believe it or not, even that is easier said than done. It can actually be quite difficult.

Most auto parts stores only carry wire based on low price point. It is typically PVC jacketed, and only rated to 80 degrees C. GM recommends (and requires their partners) to use CROSS-LINKED POLYETHYLENE jacketed wire (denoted by _XL, like "SXL", where XL stands for cross linked) for under hood and under body applications, with a temperature class rating of 125 degrees C. The best wire I've every been able to find locally without special ordering it is only rated to 105 degrees C. There is a reason why GM and Ford issue bulletins to upfitters stating that to have their modifications approved, the wire needs to be 125 degrees C.

I think that's enough for now. You should be well on your way to a factory quality installation with the wiring diagram and the parts print. I never liked the aftermarket kits either, including the vaunted "Painless" kits. Like you, I prefer to follow as much OEM engineering as possible. It can be "painful" to do sometimes though.