Vuk

This factory setup will charge them both when the motor is running, I am just confused with the batteries begin disconnected during cranking. This may be a feature on these model years because the BCM can shut down stuff if the voltage gets too low to disturb cranking? But what would be the purpose for the factory aux battery then, if this is the case? I will have my own accessories, that is OK for me, but what would the factory-intended purpose be? Was the BCM software updated with this feature starting from 2016 when the aux battery package was not offered any more? Is this maybe the reason why the tray is replaced with the dummy version (that is, the BCM takes care of over-discharge so the aux battery is not as necessary any more)? This is just me thinking why it would disconnect the aux battery during cranking.

The trays differ in two things. One is the hole for the retainer bolt - you can easily put a rivet nut there and you would be done. The second difference is the lip on the opposite side of the battery that holds the rear in (you lower the battery into the tray, you slide it towards the driver seat, the bottom edge of the battery locks into the lip on the rear, and then you put the retainer over the front edge). If I were to do this again, I would modify the old tray (now I found another project to use the old tray).

I am just finishing up my factory-style setup on my 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 contains this within the harness). It comes with the relay that controls the battery isolator ("secondary auxiliary relay"). It also includes the auxiliary battery positive terminal with a fuse holder adjacent to the terminal (populated with a 125A fuse), however, it does not come with the cover for this single-fuse box (part # for the cover is 22945779). If you would like to directly draw high gauge cables to accessories (e.g., inverter), you can get 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 (just take the battery terminal off of the single fuse holder and set it on the 3-fuse block). In that case, the fuse block 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 (as seen in photos above), 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 to complete my setup). 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. Battery tray part # is 22989633, retainer is 14005061, and the retainer bolt is 11519527, as mentioned here earlier. 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) from the harness, 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 (that is the "Run Ignition 3 Voltage" signal). 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, so just adding the terminated lead was enough. 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!