Factory dual battery wiring

[Daveo91Burb]

Anyone have any wiring diagrams or pics of their factory dual battery setup? I am finally getting around to installing the setup from my '90 parts Burb in my '91 which didn't come with that option. This is the harness from the parts rig - particularly interested in what the two small gauge black wires connect to. Also where the relay and junction block are mounted and what the negative battery cable looks like as that seems to be the one thing I'm missing. But I do have the main battery cables from the parts rig that I could use.

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[chengny]

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[Daveo91Burb]

Perfect - thanks! This is exactly what I need! The last diagram showing where everything is installed will be particularly helpful. What manual did these come from?

I was playing around with the relay tonight. 12 volts applied between the two small black wires made the relay click so I think it's working. Just need to find that negative cable now. I probably have it somewhere. If not, I should be able to use the extra one I have for the primary battery.

The battery in my '76 Corvette recently failed prematurely. Fortunately it was an Interstate from Costco and it was covered under full warranty. I also have an Interstate from Costco in the burb and the other night I noticed they are the exact same battery. Same fitment code, series, even Costco item #. So long story short, I'm using the Vette's failed battery as an opportunity to add a second batt in the burb! I'll put the brand new one in the burb and buy a second identical one from Costco and put that in the Burb as well so they are as close a match as possible. Vette will get the slightly older batt. (I tried this rationalization with my wife but I basically just got a "whatever" - not sure she got the whole silver lining part of the Vette's bad battery)

 

[adamj]

I'm not a wiring expert, but looking at that wiring diagram, it doesn't look like the best way to wire dual batteries. I know it'll be easier to use the factory wiring, and the stuff you have (although quite thin gauge) looks like it's in great condition! However, if you're going to be really in need of a dual battery setup (running accessories off the aux battery alone, draining and recharging, etc.) then I would go with some new cable mains (4 AWG minimum) and get a proper battery isolator (and also a deep cycle or AGM battery).

But if you're just looking for some extra cranking power in cold weather startups, then this should be just fine.

 

[Daveo91Burb]

I'm not a wiring expert, but looking at that wiring diagram, it doesn't look like the best way to wire dual batteries. I know it'll be easier to use the factory wiring, and the stuff you have (although quite thin gauge) looks like it's in great condition! However, if you're going to be really in need of a dual battery setup (running accessories off the aux battery alone, draining and recharging, etc.) then I would go with some new cable mains (4 AWG minimum) and get a proper battery isolator (and also a deep cycle or AGM battery).

But if you're just looking for some extra cranking power in cold weather startups, then this should be just fine.

Yeah, I wish the factory stuff was bigger, but I think I'll stick with it for now. I don't have a winch or some mega stereo system, but I do have a few lights that I will probably move over to pull off that battery directly. I really just want to have the security of an extra battery. As I understand it, the aux battery will only tie into the main system when the key is in ACC or RUN, unless there are accessories that are connected to it before the relay. This will 1) let the aux batt charge when the main batt is charging 2) add to the overall capacity of the system while idling, driving, or key is in ACC. and 3) isolate batteries from each other when key is off. Also as I understand it, the aux battery will not really help with starting since the starter pulls directly off the main batt. Although it helps indirectly by adding overall capacity to prevent main battery draw down from accessories. But I'm not a wiring expert either, so someone please correct me if I've got my assumptions wrong.

 

[HotRodPC]

Just a heads up in case you're not aware. I've been told when you run dual batteries, you should always get identical batteries and replace them as a pair also. Apparently it has to do with your stronger battery will reduce itself to match the weaker battery. So if you get an older battery and replace 1 new one, then it will drop to the older battery's equal. Not sure how true this is. I'd think if the batteries were isolated properly it shouldn't matter.

Since my K10 was previously 6.2 Diesel and has 2 battery trays, I"m going to be running 2 batteries too since I"ll be running extra off road lighting, winch and air compressor for the front Air Locker and air up tires when I leave the trails.

 

[Daveo91Burb]

Yep my two batteries will be identical and same vintage. Main one is brand new - haven't even run it yet and heading to Costco today to buy the aux.

But I agree, if they're isolated when key is off it really shouldn't be a problem - that's what the OEM relay does


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[Daveo91Burb]

So I got this all installed and working - I think it's pretty factory judging from the wiring diagram and install sheet, except for the fuse block I added. Moved my fog light relays over and sourced them directly from the new fuse block which is fed directly from the aux battery, prior to the relay which ties the two batteries together (and allows aux to charge) when key is in ACC or RUN. Eventually I'll move some other accessories over to the new block as well, such as my alarm system and a source for my AC inverter, both of which operate when key is off. The advantage here is that those accessories can't run the starting battery down when key is off.

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[HotRodPC]

Looks Legit !!!

 

[highdesertrange]

couple of hints, the battery of the same age, type applies when they are hard wired together. like on a diesel, when on a solenoid dual battery system it doesn't matter. next those factory wires for the dual battery are way to small. for that matter the factory charge wire for a single battery is way to small and goes a roundabout way to get to the battery. if you were to run a heavy wire right off the back of the alternator to the positive post of the main battery the improved charging is noticeable immediately. then run the same size large wire off the back of the alt to the aux battery solenoid and from the solenoid to the aux battery will make a huge improvement. 8 gauge is good 6 is better. highdesertranger

 

[Daveo91Burb]

couple of hints, the battery of the same age, type applies when they are hard wired together. like on a diesel, when on a solenoid dual battery system it doesn't matter. next those factory wires for the dual battery are way to small. for that matter the factory charge wire for a single battery is way to small and goes a roundabout way to get to the battery. if you were to run a heavy wire right off the back of the alternator to the positive post of the main battery the improved charging is noticeable immediately. then run the same size large wire off the back of the alt to the aux battery solenoid and from the solenoid to the aux battery will make a huge improvement. 8 gauge is good 6 is better. highdesertranger

Thanks for the info. On the no need for batteries to be identical if using solenoid: totally agree. But since I was replacing a battery in my other car that used the exact same series and fitment, I decided it couldn't hurt to make them identical. i.e. it cost me no extra to do it that way. But good info for others doing this project.

Regarding the factory wiring being too small: are you saying GM undersized it or that I installed it incorrectly? Not trying to be a smartass, but it's just that I didn't take pics of this system on the parts rig ('90 V2500 suburban, gas) before I removed it and I was also wondering about the small gauge wire on the positive post. Am I missing part of the factory setup between alternator and positive post? I think I'm just fine on the usage side of things, but I see what you're getting at on the charging side as it would charge faster with a bigger wire.

 

[highdesertrange]

yeah you didn't do anything wrong. you just did what the factory did. yes GM used way to small wire on the charging circuit so did every other manufacturer. just the way they did it. it's kinda like the headlight wire circuit, it works but an upgrade makes a huge difference. highdesertranger

 

[HotRodPC]

couple of hints, the battery of the same age, type applies when they are hard wired together. like on a diesel, when on a solenoid dual battery system it doesn't matter. next those factory wires for the dual battery are way to small. for that matter the factory charge wire for a single battery is way to small and goes a roundabout way to get to the battery. if you were to run a heavy wire right off the back of the alternator to the positive post of the main battery the improved charging is noticeable immediately. then run the same size large wire off the back of the alt to the aux battery solenoid and from the solenoid to the aux battery will make a huge improvement. 8 gauge is good 6 is better. highdesertranger

Seems legit way of doing it to me too. I also agree, heavier wire is best for certain, and make sure if it's routed through any sheet metal to use grommets.

Thanks for confirming about same battery age, size and CCA. I was pretty certain if an isolator and/or solenoid was used to keep the 2 batteries separate from each other it didn't matter.

 

[Daveo91Burb]

Yep, thanks for all the tips. Upgrading some of that wiring with bigger gauge stuff is added to the to-do list. Probably will do the headlight wiring at the same time and convert them all to full relay-operated. I already have the low beams operated via relay when the high beams are on, need to go all the way.


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[HotRodPC]

Another thing you might want to check if it's possible, is to find out which alternator you have on your rig. It could be a 63amp or a 94amp. Hopefully the 94amp. If it's the 63 consider upgrading to a 94 when the 63amp takes a dump. Some guys want to do the 105amp upgrade. IMO, there isn't much difference in the 94amp to the 105amp, but the 105amp is a bigger housing then you get into bracket modifying, possibly belt change and/or pulley swapping.