Connecting Radio To AUX Battery

Connecting Radio To AUX Battery

Postby kirklaut [OP] » June 30th 2015, 4:40pm

I have a dual battery system set up (AGU Deep Cycle Dual Purpose 75ah & the main starter battery) with both batteries receiving a charge from the alternator. The isolator I used allows me to start the van from the deep cycle if the starter battery goes dead but everything else (interior lights, radio, 12V outlets) is still only connected to the starter battery)

I have since added a 12V outlet and inverter directly to the AUX battery and was thinking of wiring my interior lights directly directly to it as well to take better advantage of the dual battery set-up.
However, while considering this I think what I would really like is to be able to run my radio off of the second battery. I imagine if I found the power for the radio I could just run the wires back to the AUX battery but then I worried the radio wouldnt turn on-off with the start of the van. I know I could get in the habit of manually turning it off and on but I can almost guarantee times when the radio stays on for days because the volume is set to zero and I forget its on. Im not sure if its possible but if so I would be very interested in find out out how to connect it to both batteries...still connected directly to the vans original wiring so it turned off and on with the van but also connected to the second battery so that I could press the power button and run the radio without having to turn the key....

Is this doable?
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Re: Connecting Radio To AUX Battery

Postby gavio » June 30th 2015, 5:39pm

I'm wanting to do the same thing, but I haven't gotten into it yet...

My last van was from the 80's and didn't have a Body Control Module running things... I used an aftermarket stereo and all I did was hook up the main power wire to the aux battery and the memory wire to the starting battery - It worked like a charm, turned on and off with the ignition but main power was draining from the aux battery.....

On the Astro, I am concerned about whether you can separate the feeds that easily without confusing the BCM - computer interfaces make me nervous.... I'll be watching to see how this turns out...
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Re: Connecting Radio To AUX Battery

Postby kirklaut [OP] » June 30th 2015, 6:46pm

....maybe Ill just give that a shot....

i mean, whats the worst that would happen?

I installed an aftermarket radio which required crimping together 12-15 wires based on color. How do I know which wire is the main power? Ill start digging around in there this afternoon but maybe someone can speed up the process with a description or pictures...
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Re: Connecting Radio To AUX Battery

Postby gavio » June 30th 2015, 8:28pm

I just looked, according to my FSM, the yellow wire going into the factory radio harness is the ignition feed, which presumably is the one controlled in reality by the BCM, and the orange wire is the straight 12v feed.... I have no clue how the internals of the radio are wired, so it could mean either:

a) the yellow wire controls on/off/memory functions, while the orange is main power to the amp and mechanicals,

OR

b) the yellow wire is on/off/main power, while the orange is only the memory feed (for the radio to remember your presets and passcode and all)

If it's option (b), then I think connecting to the aux battery will mean you need to remember to turn it on and off yourself....

If it's option (a), then I think it just might work the way you want.... And hopefully the BCM won't send a weird signal to the flux capacitor, causing a core breech and, ultimately, loss of driveshaft fluid...
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Re: Connecting Radio To AUX Battery

Postby kirklaut [OP] » July 1st 2015, 3:22pm

So here is what I've found. All similar but slightly different.

Based on these, I am thinking of trying to connect the YELLOW to the aux.

Thoughts...
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Original Poster [OP]
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Re: Connecting Radio To AUX Battery

Postby gavio » July 1st 2015, 5:35pm

If you have a multimeter, I'd recommend using it to test which one of those leads draws the most current, then you'll know for sure what to do. Another clue might be in the size of the wires - the one carrying the real power will often be much thicker.... If the main power is running through that red wire, then it'll have to be connected to the aux battery, too, to keep from draining the starting batt, and then you'll lose the on/off with the ignition functionality....

If you can't test it, it's a fair guess that the red wire just turns it on and off - it's how my old one was wired, and connecting the yellow to the aux batt will do what you want...

Sadly, if you can't test it, you'll not know for sure until the first time you leave it on by accident :oops:
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Re: Connecting Radio To AUX Battery

Postby kirklaut [OP] » July 1st 2015, 7:29pm

Yellow and Black are the thickest.

Feeling optimistic

I probably wont have a chance to hook it up until early next week but I will update when I do.
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Re: Connecting Radio To AUX Battery

Postby kirklaut [OP] » July 18th 2015, 6:13pm

I tried connecting the yellow "power" wire to my aux and got no results. I tried connecting both the power and ground to the battery. Still no results.

Even with this set up and the key turned to the "on" position I couldnt get the radio to turn on.

Kind of bummed it didnt work out but I dont want to mess with any of it too much more....
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Re: Connecting Radio To AUX Battery

Postby gavio » July 18th 2015, 8:23pm

Sorry it didn't work out... Thanks for reporting, though, now I know not to try THAT....

It probably confused one of the computers involved...:shrug: ....
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Re: Connecting Radio To AUX Battery

Postby AstroWill » July 18th 2015, 9:57pm

If battery grounds are not tied together you will have to use one battery for both the yellow and the red wire, using the battery that you are grounding to, they do make switches specifically for this purpose in the RV industry.

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Re: Connecting Radio To AUX Battery

Postby gavio » July 18th 2015, 10:13pm

If battery grounds are not tied together you will have to use one battery for both the yellow and the red wire


Correct me if I'm wrong, but if both batteries are grounded to the chassis, isn't that the same thing?
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Re: Connecting Radio To AUX Battery

Postby AstroWill » July 18th 2015, 10:19pm

Yes, that would work as well.

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Re: Connecting Radio To AUX Battery

Postby Lumpy » July 18th 2015, 10:34pm

This shouldn't be that difficult.

Is this an OEM GM/Delco radio?


What does make it difficult that sometimes different sources of wire color info give you different color schemes. Aftermarket devices might use BLK for power or for ground or for something unrelated entirely. Same with any other color. Even battery primary cables are often both black.

Generally (but not always) On the radio -

YEL, RED or ONG - In various combinations one or more of those colors are +12v ALWAYS HOT or +12v ACC/RUN.

It's "nearly" always safe (but not always) to assume that BLK is ground.

For what it's worth, in Gen I vans -
BLK is ground
YEL is +12vdc ACC/RUN
ONG is +12vdc ALWAYS HOT
GRA is +12vdc DASH ILLUMINATE

Then just to keep things confusing, GRA is also one of the speaker wire colors.

In general, but not always, lots of GM cars are -
ONG is +12vdc ALWAYS HOT
RED is +12vdc ALWAYS HOT
YEL is +12vdc ACC/IGN
BLK is -12vdc or GROUND

Any of those colors with a stripe are something else, sometimes not at all related.

Trailer wires use some of the above colors for an entirely different purpose.

So it's almost never safe to assume "My YEL wire does this up here under the dash, it must do the same thing back here by the flux capacitor cooling fan".


Try This -
Whichever two wires (on the RADIO not the van) are hot and switched (YEL, RED or ONG or something else) connect them both to BAT+. If BLK is radio GROUND, connect BLK to BAT-. That should allow you to manually turn the radio on and off at the radio's power switch. If you can get to that point, we can figure out a way to power it on in whatever manner you want - IGN, remote switch, automatic switchover relay, whatever.


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Re: Connecting Radio To AUX Battery

Postby bunce1260 » December 3rd 2015, 9:09pm

Anything to report back?
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Re: Connecting Radio To AUX Battery

Postby TaxiVan » December 3rd 2015, 9:36pm

The stereo uses two 12V wires and a ground. One 12V is a constant to keep memory presets and the other is a switched 12V from ACC. I would simply splice into the switched 12V ACC input and use a diode to keep it from feeding back into any possible connection to the BCM. I seriously doubt the stereo is controlled by the BCM, but I could be wrong.
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