How do I correctly wire an auxiliary battery 99 Suburban using existing GM equip??

[DeadheadNM]

I've got the 99 Suburban and an extra battery. The Sub came with an aux (LH) battery tray and I see attached to the under hood fuse block there are two battery terminals labeled "Aux A" and "Aux B". How do I wire up the aux battery without ruining the wiring?

My hope is that by doing so I have one battery dedicated to starting the Sub while the other can run equipment when the engine is off and drain with no consequence for starting. I've installed OEM aux battery setups in my 1972 Blazer and K20 - just not at all familiar with newer model trucks and couldn't find a related thread. Thanks, Pete

[Mr_Rich]

I did this many years ago with my '89 K1500. It's been so long that I doubt the factory parts are still available. There was a wiring harness and relay that mounted next to the windshield washer jar on the driver's side fender. I had to open up a hole on the firewall to connect part of the harness to the fusebox. It was all done with factory parts in the factory routing locations. It was kind of tricky since the diagram is not in the same orientation as the fusebox. It works great and the battery stays charged. I'd provide pictures except for the fact that my truck is getting some paint these past couple of weeks.

[DeadheadNM]

Originally Posted by Mr_Rich

I did this many years ago with my '89 K1500. It's been so long that I doubt the factory parts are still available. There was a wiring harness and relay that mounted next to the windshield washer jar on the driver's side fender. I had to open up a hole on the firewall to connect part of the harness to the fusebox. It was all done with factory parts in the factory routing locations. It was kind of tricky since the diagram is not in the same orientation as the fusebox. It works great and the battery stays charged. I'd provide pictures except for the fact that my truck is getting some paint these past couple of weeks.

Thanks Rich - I may drop by a local Chevy dealer and see what if any schematics the parts guys can produce. I'll let them know what I'm after and see what I can scare up. With the trailer package, it looks ready to go for the aux battery from GM - it may be as easy as just getting pos/neg wires and bolting the pos to the correct terminal on the fuse block under the hood. Of course life's rarely that simple....

[Mr_Rich]

It's actually for the camper package. The diesel trucks also had an aux. batt. for other reasons, I think. There's an extra 10 ga. lead that goes from the aux. batt. to the terminal under the plastic cover on the pass. side firewall.

[83GMCK2500]

Aux A & Aux B are NOT for connecting the battery. Those posts are there for things that you might ADD. There is a factory option or two that use them, I can't remember what right now. Camper/Trailer wiring is the most commonly added feature.

Give me a few minutes and I think I can have your wiring diagram. Help me out here, 350/454, 1500/2500?

[DeadheadNM]

Originally Posted by 83GMCK2500

Aux A & Aux B are NOT for connecting the battery. Those posts are there for things that you might ADD. There is a factory option or two that use them, I can't remember what right now. Camper/Trailer wiring is the most commonly added feature.

Give me a few minutes and I think I can have your wiring diagram. Help me out here, 350/454, 1500/2500?

Thanks guys! Vortec 350 1500 4wd...

[dragginmetal]

Here's some info that might help you out.

99 Sub K1500 5.7l
1.pdf
2.pdf
1 of 6.pdf
5 of 6.pdf

[dragginmetal]

General 88-98 info

[DeadheadNM]

Huge help - thank you!!

[dragginmetal]

No problem. ....That's the best could do. I have never been under the hood on a 96-99 suburban. If you need any more info, just let me know what you need and i will try and look it up.

[DeadheadNM]

Will do! That gives me a lot to go on. If a member has this setup already in use some pics would be great. Thanks again, Pete

[Mr_Rich]

You may find this wiring diagram helpful. This is what I used when I wired my aux battery in my truck. The tricky thing about this diagram is that the convenience center is in a different orientation on the truck than it is in the diagram. It caused me to pause a bit when I was wiring up the battery. I had the advantage of using the factory harness which might not be available any more.

[DeadheadNM]

Originally Posted by Mr_Rich

You may find this wiring diagram helpful. This is what I used when I wired my aux battery in my truck. The tricky thing about this diagram is that the convenience center is in a different orientation on the truck than it is in the diagram. It caused me to pause a bit when I was wiring up the battery. I had the advantage of using the factory harness which might not be available any more.

Appreciate the pic - I was hoping that the local GM parts folks might have a part # for an aux battery harness to make this a plug and play project but they did not. Adding the OEM aux battery equipment was relatively straightforward in my 1972 4wds - things got complicated over the years at GM!

[dragginmetal]

Mr_Rich, What's the name of that book. I need to get that one.

[txgp17]

I added a second battery to my 99 K3500. But I just wired mine in parallel. There's a heavy gauge wire that comes from the passenger side battery, traveling on top of the radiator shroud to the driver's side, turns by the washer fluid reservoir neck, and goes to the under hood fuse box. For lack of the proper term, I'll call it the feed wire.

I installed my driver side battery, and cut the feed wire where it could connect to the positive terminal on the driver side battery, and put a terminal on it to fit under a side terminal connector. Then I replaced the amount of wire I'd cut out with the largest diameter wire I could fit in the original location, I think I used 4 gauge.

I grounded the driver's side battery on one of the bolts that holds the A/C compressor on. I verified that it was a good connection by starting the truck a few times with just that ground wire connected.

So the passenger battery uses OEM wiring, and the driver's side battery has a heavy gauge wire going post-to-post, and the OEM wire feeding power to the under hood fuse box.

I did this in January of 2004, and never had a problem with it.

Granted, this is parallel wiring. If you wanted to isolate them, it gets more complicated.

[Mr_Rich]

Originally Posted by dragginmetal

mr_rich, what's the name of that book. I need to get that one.

1989 c-k pick-up truck electrical diagnosis and wiring diagrams
st-375-89 edd

[DeadheadNM]

Originally Posted by txgp17

I added a second battery to my 99 K3500. But I just wired mine in parallel. There's a heavy gauge wire that comes from the passenger side battery, traveling on top of the radiator shroud to the driver's side, turns by the washer fluid reservoir neck, and goes to the under hood fuse box. For lack of the proper term, I'll call it the feed wire.

I installed my driver side battery, and cut the feed wire where it could connect to the positive terminal on the driver side battery, and put a terminal on it to fit under a side terminal connector. Then I replaced the amount of wire I'd cut out with the largest diameter wire I could fit in the original location, I think I used 4 gauge.

I grounded the driver's side battery on one of the bolts that holds the A/C compressor on. I verified that it was a good connection by starting the truck a few times with just that ground wire connected.

So the passenger battery uses OEM wiring, and the driver's side battery has a heavy gauge wire going post-to-post, and the OEM wire feeding power to the under hood fuse box.

I did this in January of 2004, and never had a problem with it.

Granted, this is parallel wiring. If you wanted to isolate them, it gets more complicated.

Good deal - this may be a good stopgap approach until I can get the systems isolated....I don't know why GM kept ALL the 12v power supplies hot with the car ignition off...

[Already Gone]

I have factory installed auxiliary batteries on my 99 Cop Tahoes and can take some pics and post them on here if you think they will help. It'll be a day or two until I can get to the garage where they are stored to take the pictures.

[DeadheadNM]

Originally Posted by Already Gone

I have factory installed auxiliary batteries on my 99 Cop Tahoes and can take some pics and post them on here if you think they will help. It'll be a day or two until I can get to the garage where they are stored to take the pictures.

Greg - I greatly appreciate that! No rush. Thanks, Pete

[Already Gone]

10-4, anything particular you need to see?

[83GMCK2500]

Sorry for the delay, computer wasn't cooperating. Here is what I can provide. Also threw in the DUAL battery wiring, so you can see how it differs. Quite a bit really, they're just in parallel on dual battery vehicles.

[DeadheadNM]

Originally Posted by Already Gone

10-4, anything particular you need to see?

Pos lead from aux battery to wherever it goes (J-block) and that lead followed back if poss. Thx!

Originally Posted by 83GMCK2500

Sorry for the delay, computer wasn't cooperating. Here is what I can provide. Also threw in the DUAL battery wiring, so you can see how it differs. Quite a bit really, they're just in parallel on dual battery vehicles.

Thx!! Will review...

[83GMCK2500]

Originally Posted by DeadheadNM

Appreciate the pic - I was hoping that the local GM parts folks might have a part # for an aux battery harness to make this a plug and play project but they did not. Adding the OEM aux battery equipment was relatively straightforward in my 1972 4wds - things got complicated over the years at GM!

Your Parts guy needs to go back to school...took me, under a minute to find this in the Electronic Parts Catalog...way more time to type it up.

#1 - 15354169 - Cable, Aux Bat Pos
#2 - 12338130 - Nut, Hex 5/16-18X.25 286M POR
#3 - 19115561 - Bolt, Hex Hd, 3/8-16X13/32, 1/4 THD, 1 5/32 TOTAL LG, 51/64 OD
#4 - 00136857 - Washer, External Tooth LK 7/16
#5 - 12190685 - Cable, Aux Bat Neg
#6 - Same as #4
#7 - Same as #3
#8 - 12135196 - Relay, Aux Bat
#9 - 12160765 - Cover, Bat Pos Cbl J/Blk

#10 - See below...

#11 - 15551605 - Bolt, Hwh Tap, M6.3x1.27x20, 18.5OD, TR PT1018, AL
#12 - 11516079 - Nut, Prevailing Torque Type W/WA Insert (M6x1 THD8.8 THK)
#13 - 88862249 - Connector, Pwr Dist Blk (ACDelco #PT2330)




#10 is a pistol, it's the cable that connects the relay to the battery. It is very RPO dependant, depending on what options you have this cable varies in length and gauge.

[DeadheadNM]

Devin - much appreciated! I'll work on tracking down the components and get #10 squared away. I may hit some local salvage yards on the off chance that a Sub is sitting with all the pieces intact. My Sub came with a 100 amp alternator - imagine I'll need to bump that up to 140 once I get both batteries installed.

[txgp17]

Originally Posted by DeadheadNM

...imagine I'll need to bump that up to 140 once I get both batteries installed.

I don't think so. Having two batteries doesn't mean you'll consume anymore electrical energy. But if both batteries are drained significantly, any alternator will struggle to maintain proper voltage.

Personally I consider the extra battery to act a "buffer" for heavy electrical loads. It allows to alternator to work moderately for a longer duration to recharge the batteries, rather than working to it's limits for a short duration.