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txgp17 · 10-19-2013, 04:14 PM

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.

10-19-2013, 04:14 PM	#15
txgp17 Registered User Join Date: Mar 2013 Location: Kernersville, NC Posts: 8	Re: How do I correctly wire an auxiliary battery 99 Suburban using existing GM equip? 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.