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Have a System in your truck ? Have a snow plow or wench on the front ? extra lights and inverters ? Whatever you want it for, and NOT use your main battery.
 

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I did the Dual Battery upgrade on my 2013 1500, I also upgraded all the battery cables.
Now after turning off the motor, but leaving the key in the accessory position, I get a warning that the battery is low and I should start the truck.

Has anyone else seen this or know of a fix?

I'm guessing it's because of the second battery and new ground cables. The main ground cable goes through a sensor, so I believe it's just not reading correct now.
 

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Hello, all! Thank you for a great thread!

Any chance someone knows the number for the original ACDelco auxiliary battery harness that would fit a 2016 Sierra 1500? I am trying to save some time.

Thanks a lot!
 

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I managed to find the information I was looking for in my previous post, and am finishing up my factory-style setup on a 2016 Sierra 1500.

The harness part # for this age is 23273450. It replaces the original wire that runs from the primary battery to the underhood fuse box. It comes with the relay that actuates the bigger relay that disconnects the batteries (i.e., secondary auxiliary relay), and includes the auxiliary battery positive terminal with a 125A fuse holder adjacent to the terminal. However, the cover for this single-fuse box is a separate part # 22945779. If you would like to directly draw high gauge cables to accessories (e.g., inverter), you can buy the 3-fuse holder from older models (19116352 and cover 15881616) so you get a 100% factory install with provision for accessories. This 3-fuse holder can replace the single fuse holder that comes with the aforementioned harness and in that case sits on the battery just like the single-fuse box would. The distribution block on the primary battery already has a blank 125A spot for the auxiliary battery harness, so no modifications are needed there - just some nuts (should be 21021808).

Auxiliary battery negative terminal with the wire should be 84354708 (I am still waiting for this last part).

The secondary auxiliary relay part # is 12135194. You will have to use either self-tapping screws or rivet nuts to mount it to the firewall, as described earlier.

Battery tray part # is 22989633, retainer is 14005061, and the retainer bolt is 11519527.

Next, you need the "X158 Auxiliary Battery Harness to Engine Harness" that supplies ground, (+), and the signal for the relay to the aforementioned auxiliary battery harness (if you don't want to make the connector yourself). Service connector part # is 19367564. If you want to go full-factory, you can get violet/brown and red/white wires online. The black (ground), I connected to the ground post on the firewall where the relay is mounted.

The violet/brown connects to pin 42 of "X115 Engine Harness to Body Harness" connector near the underhood fuse box and the auxiliary battery. The "body" side of the connector is very accessible and there is already a violet/brown wire that you can tap into. The red/white needs to go to pin G6 of connector X2 of the underhood fuse box - there was no pin in there so I used the terminated lead 19301767. I already had the F52UA fuse installed - that one will supply power for the auxiliary relay.

Everything works but I am surprised that the relay disconnects the batteries during cranking. Can someone confirm how the system operates? I was expecting the auxiliary battery to "help" during the cranking. I can clearly hear the relay engage when the key is in ON, but disengages during cranking, and engages again when the cranking is over.

Thank you!
 

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Step 6.
Now its time to tackle the harness that makes all this work. Start with the male connector that will plug into the one we zip tied to the alternator wire. Here is the sequence on how to make these connectors. Slide the seal onto the wire, crimp the wire to the terminal, slide the seal up to the terminal, crimp the seal to the end of the terminal, insert your terminals and plug, and attach the TPA. Use same pin out used for the male connector. For this side you need TPA (P/N 12160480), Connector (P/N 12160482), 3 terminals (P/N 12048074), 3 seals (P/N 15324976), and one plug (P/N 12059168).










This is what you need from the relay kit


You need to double up the ground terminal


From left to right you have the red wire from the engine harness, it goes to pin 30 on the relay. Orange wire from harness goes to pin 86 on the relay, black wires go to pin 85, and the 2nd red wire goes to the battery isolator.


So at this point we should have two wires coming off the relay. A red and a black. These two wires are going to go to the connector for the battery isolator. For that you'll need TPA (P/N 12052634), connector (P/N 12052641), 2 terminals (P/N 12160223), and two seals (P/N 15324976). The red/wh wire from the relay goes to Pin A and the black wire goes to Pin B. Once that is connected I loomed all the wires and ended up with this.


Plug it all in and clean everything up and you are done.




You'll need these little gems to screw onto the studs on the firewall above the motor. They're called speed nuts. They're the only thing that will thread onto the factory studs. I forget what size they were. They were the only black ones in the box.


Conclusion:
This is a very doable project. It does take some time, but the wiring is solid and looks like a pro did it.
This write-up was invaluable. It was THE source for my successful OEM-like install of the actual TP2. Excellent work. One tiny question - for the life of me I cannot locate those "speed nuts" for the harness up on the firewall. I've tried every nut-like creation I could get my hands on from Ace Hardware with no luck. What a crazy fastener. Did yours come with something?
 

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This write-up was invaluable. It was THE source for my successful OEM-like install of the actual TP2. Excellent work. One tiny question - for the life of me I cannot locate those "speed nuts" for the harness up on the firewall. I've tried every nut-like creation I could get my hands on from Ace Hardware with no luck. What a crazy fastener. Did yours come with something?
I didn’t use them. I just zip tied the new cable to the existing harness. You don’t really notice it at all.
 

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2001 GMC Sierra 2500HD CCSB
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This write-up was invaluable. It was THE source for my successful OEM-like install of the actual TP2. Excellent work. One tiny question - for the life of me I cannot locate those "speed nuts" for the harness up on the firewall. I've tried every nut-like creation I could get my hands on from Ace Hardware with no luck. What a crazy fastener. Did yours come with something?
They are called a "thread cutting nut" if you search online you will find them easier. Example here https://www.amazon.com/Dorman-Help-...dp/B000CO934I/ref=psdc_15706641_t3_B07HKSF1L5

I found them at my local hardware store, but this particular store has the full isle of bolts/nuts/washers selection. I can't remember the exact size I think it was like an 8mm or 9mm. Just buy a few different sizes that look close and take back what you don't use.
 

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They are called a "thread cutting nut" if you search online you will find them easier. Example here https://www.amazon.com/Dorman-Help-...dp/B000CO934I/ref=psdc_15706641_t3_B07HKSF1L5

I found them at my local hardware store, but this particular store has the full isle of bolts/nuts/washers selection. I can't remember the exact size I think it was like an 8mm or 9mm. Just buy a few different sizes that look close and take back what you don't use.
Thanks - now I can put a name to it. Our Ace Hardwares here in Phoenix have large fastener sections including automotive which are impossible to find. I'll run that name by them.
 

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Step 6.
Now its time to tackle the harness that makes all this work. Start with the male connector that will plug into the one we zip tied to the alternator wire. Here is the sequence on how to make these connectors. Slide the seal onto the wire, crimp the wire to the terminal, slide the seal up to the terminal, crimp the seal to the end of the terminal, insert your terminals and plug, and attach the TPA. Use same pin out used for the male connector. For this side you need TPA (P/N 12160480), Connector (P/N 12160482), 3 terminals (P/N 12048074), 3 seals (P/N 15324976), and one plug (P/N 12059168).










This is what you need from the relay kit


You need to double up the ground terminal


From left to right you have the red wire from the engine harness, it goes to pin 30 on the relay. Orange wire from harness goes to pin 86 on the relay, black wires go to pin 85, and the 2nd red wire goes to the battery isolator.


So at this point we should have two wires coming off the relay. A red and a black. These two wires are going to go to the connector for the battery isolator. For that you'll need TPA (P/N 12052634), connector (P/N 12052641), 2 terminals (P/N 12160223), and two seals (P/N 15324976). The red/wh wire from the relay goes to Pin A and the black wire goes to Pin B. Once that is connected I loomed all the wires and ended up with this.


Plug it all in and clean everything up and you are done.




You'll need these little gems to screw onto the studs on the firewall above the motor. They're called speed nuts. They're the only thing that will thread onto the factory studs. I forget what size they were. They were the only black ones in the box.


Conclusion:
This is a very doable project. It does take some time, but the wiring is solid and looks like a pro did it.
Looking at the same project for my Mrs. Suburban. I’ve looked in the other forums and stumbled on this post looking up something completely separate for my Sierra.
We’ll done my man!!
 
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