OEM Auxiliary Battery Install Help

[Rob T]

I was reading on the forums on auxiliary battery installs to see what everyone else was doing. I started the install of an auxiliary battery in my XL and decided to go with all OEM parts. I sourced the part numbers from a Silverado with the same 8.1 that I have in my XL. I figured it would be easier to obtain replacement parts in case there was an issue later down the road.

The OEM install calls for a battery relay that sits on the passenger side fire wall. There is a plug that connects to this relay that is integral with the harness that houses connectors for the A/C accumulator, A/C low pressure switch, coolant level sensor connector, and MAF. I don’t have this plug in my harness since the truck didn’t come originally equipped for dual batteries.

I haven’t fully connected all the cables, since I need to get behind the driver’s side firewall to connect the ground cable to the existing ground connection on top of the engine near the bell housing, and the positive wire that connects the battery relay to the hot side of the fuse box.

I was wondering if anyone has done the OEM install and if this plug is necessary for the auxiliary battery to charge or function? I can source the plug, and by looking at the wiring schematics, there is a connection to the fuse box via fuse and relay, but not sure where or how to connect? The schematics are unclear.

Can anyone chime in on what to do?

Any help would be greatly appreciated. Thanks in advance.

 

[TacHoe]

in for some help on this as well!

 

[Rob T]

Schematic

Looking through a factory service CD that I purchased for a wiring schematic that would show how the wiring would run from the battery relay to the fuse box and this is what I found.

The hot wire connects to the 4WD fuse in the fuse box, at least that's what I see in the diagram.

Could this be correct? How would I go about wiring this?

 

[Rob T]

Wire 241

Ok. I think I figured it out. On the schematic, there is a number (241, Ignition 3) shown. I was thinking it was to a field or group related the fuse box. Just out of curiosity, I searched the CD for the junction box connector diagrams and looked for 241 to see if there was a relation, and there it was, the 4WD power wire is at wire 241 in the harness, and also shown in the fuse box diagram.

When I looked up the harness schematic for the XL, it differs somewhat from the Sierra / Silverado, since the XL doesn't have the auxiliary battery set up.

The 241 wire is present in the XL harness, but it does not connect to anything in the fuse panel. Tracing the wire through the fuse box, there is a plug set, #C100 that goes from under the dash, through the firewall to a harness from the engine side. From the engine side, PIN C is where 241 should be. To the dash side of the harness, there is no wire, so I think I will add a wire to the dash side of the connector where the 241 wire would be present, add a 15 amp fuse and run that to the battery relay.

The ground I will source by the fuse box since ground schematics for the 241 wire lead to ground points by the engine.

Going to order the relay connector Monday.

 

[OmarR]

Here is some good info:

http://z71tahoe-suburban.com/iboard/index.php?showtopic=20692

I hope it helps.

 

[Rob T]

Omar's link was the help I was looking for.

Thank you very much.

The install was identical to what was pictured, but Omar's pics for the C100 harness made sense of what I found in the schematics. I also learned something new about the Ign 1 and Ign 3 set ups, which I didn't think was possible.

Again, thank you.

 

[OmarR]

Glad I could help!

 

[mazdawg(Mikey)]

really helpful link omar. i asked you a question over there but if needed i can ask you here.

 

[OmarR]

Answered.