TheSamba.com :: View topic - How to wire stereo to switch between main and aux battery?

Thu Apr 06, 2006 9:27 am

This is kind of a dumb question but . . .

I want to wire my stereo so I can run it off of either the main battery or the aux battery. The deck has a yellow wire (Constant power) and red wire (ignition) Since the yellow wire has an inline fuse, I assume that is the one that draws the juice to run the deck, and the red wire just makes sure that the ignition is switched on so you can't run the stereo with the ignition off.

I guess I would need an A-B type switch (I don't know if that's the correct term) with two sets of terminals for each position - on the side used for the aux battery, the yellow and red wires could be combined since there's no ignition switch function, but on the side used for the main battery, the yellow and red wire would have to be kept separate. Or do I have to use two switches? Is there a way to do it so you don't momentarily lose power to the deck when switching between power sources and therefore lose your radio station presets?

Thu Apr 06, 2006 9:29 am

Why do you want to do this?

Thu Apr 06, 2006 9:54 am

For normal around-town driving, I want the stereo to shut off when the ignition key is off so I don't have to worry about forgetting to turn it off, but I want the ability to run it off the aux battery without having the ignition switch on for camping.

Thu Apr 06, 2006 10:11 am

Well that's kind of why you have an aux battery is so you don't have to worry about leaving it on to much. It could be done but it might be a hassel. Most radios if you interrupt the power to the yellow "memory" wire you will lose all your presets, I've yet to see one with a memory back-up.
I have the power for my radio hooked to a 12volt lighter plug, This way I can use it off AC power with a converter.
I have the yellow wire running direct to the aux battery, it doesn't draw much power.
Maybe if you could find a nice heavy duty switch and just Hooded up the red power wire, and left the yellow wire hooked up like it is or hooked to the aux battery it would be easier.

Thu Apr 06, 2006 11:18 am

The yellow wire is your constant hot. Hook it up to the aux. power.
The red wire is the main hot comming into the stereo. you could put a single switch in to do the job.

In one position, have the hot from the ignition run through to the stereo. In the other position, run a hot from the aux. batt. (could just use a jumper from the incomming yellow wire.)

In this setup, you will always have power to the unit (via yellow wire) to keep the clock and presets powered. The incomming hot that runs the unit will now swithc between 'normal' (on/off w/ key) to 'camper' (always on, drawing from aux. power).

Hope that helps.

Thu Apr 06, 2006 11:29 am

Baja, I am doing the exact same thing to mine as I hate having to turn my radio on and off manually (my Kenwood has a secret button that has be pressed a # of times before the blank face flips over exposing the radio). I have not done my new switches yet but heres the plan: When I installed the radio I wired it just as normal with the exception of running the main power wire (not the memory) back to the aux battery area. For now it is just wired up to the aux battery itself that is already back there. But when I wire in the new master switches etc.. I am putting in an extra 3 way switch. One way on will have constant power (from the aux battery) this will be for camping etc.. go the other way on the switch and it is now wired to the ignition switch for when you are just driving around town (you can pull power for that from the lead for the relay so only 1 wire needs to be pulled from the dash :D ) Just use an "on-off-on" switch, I am using some rocker style switches I found at a marine store along with marine fusebox, there will actually be a few switches for various things that I will place right where I have placed the switch and aux plug visible in this pic:

Don't get any switches with LED's in them, see that blue on the switch in the pic? Its blinding at night and the whole interior glows at night if its on! One reason along with adding more stuff, that I am changing switches out!

Thu Apr 06, 2006 12:57 pm

At this URL:

http://www.thesamba.com/vw/forum/viewtopic.php?t=154485&highlight=radio+shack

As soon as I had the auxiliary battery, I transferred the wire over to its fuse box and put the Amp on that, too. As far as I'm concerned, the main (SLI) battery runs as little as possible, for reasons of survival. But, this way, switch one way, need key, switch the other way, no radio (useful with obnoxious children), switch the OTHER way, no key required!

I've been using the radio mostly in that mode. Nice when I'm doing other work.

Best!

Thu Apr 06, 2006 11:48 pm

That's not a dumb question. I pondered that also.
You can do it with a SPST switch and just switch the main power wire as previously stated...instead of a DPDT. Then you can run the "always on" wire to either battery, doesn't matter.
I would however, use a switch with an led and mount it near your dash so the led lights up when switched to aux. If it's too bright you can always put a piece of electrical tape over it temporarily...keep a roll in the glovey. I like an idiot light close by where I can see cause I don't trust my memory.
If you really want to separate both batteries from both stereo power wires, you could install a relay. But that's overkill.

Fri Apr 07, 2006 6:17 am

.
Quote: . I like an idiot light close by where I can see cause I don't trust my memory

The fact that the stereo keeps playing when you take you key out would not be enough for you? :D

Fri Apr 07, 2006 7:48 am

lol. No it's not enough for me. I have amps that light up that I don't necessarily want running, so at low volume it can be hard to tell. If I'm camping I fade the massive light from the face plate now and then and so an indicator is needed. It's a matter of preference.

Fri Apr 07, 2006 8:57 am

northwesty wrote: That's not a dumb question. I pondered that also.
You can do it with a SPST switch and just switch the main power wire as previously stated...instead of a DPDT.

What are SPST and DPDT switches?

Fri Apr 07, 2006 10:39 am

Baja Uber Alles wrote:
What are SPST and DPDT switches?

SPST -- single pole single throw. One set of contacts, so two wires are connected together when switch is thrown.

DPDT -- double pole double throw. Two sets of contacts, so two wires get connected together, and then another set of wires get connected together (but are not connected to the first set)

Fri Apr 07, 2006 11:24 am

Would a DPDT switch accomplish this? Or would I need two DPDT switches, or is there such thing as a quadruple pole double throw switch?

http://www.thesamba.com/vw/forum/album_page.php?pic_id=267464

Fri Apr 07, 2006 1:13 pm

I didn't worry about switching the constant power to the radio. This is a minimal current draw and is only used to keep memory.

I mounted the switch on my dash. Easy to remember when I forgot to switch it off, as my radio stays on and I flip the switch.

I've ran my aux battery down with this setup (aux battery powers interior lights, inverter and my radio) and started right up from the main.

Fri Apr 07, 2006 1:45 pm

vwman, That diagram would backfeed 12volts into the ignition switch would it not? I can't see how that would work and not blow fuses or something if you left it on and kit the key! not metion that it would also send power to whatever else is on the "radio" circut off the switch.

what you want is a SPDT switch very simple-three poles off the back of the switch. hook the center pole to the hot wire of the radio, the other 2 poles get the aux and vehicle battery respectivly:

top pole---------------+aux battery
I
I
on-off-on switch-> middle pole--------------+ stereo
I
I
bottom pole-------------+switched ignition

this actually gives you three positions; throw the switch one way, you get the aux battery. Put it in the center position and the is NO power to radio. throw the switch the other way and it is now off the ignition, that way everything it TOTALLY separate of each other no if's and's or buts! I would run the memory to the vehicle battery just because that battery is less likely to dump if your out camping and forget to turn something off etc..

I have a switch in my hot little hands allthough it is rectangular rocker style; Cole hersee Co. #58027-03BP (SPDT rocker switch 25A)

Fri Apr 07, 2006 2:56 pm

OOOPS. I drew the diagram wrong. This is what I meant:

This does feed power back to the ignition switch, but the switch must be designed so that the radio (and other accesories) have their own contact. Nothing else is getting juice (at least in my vanagon).

Thu Aug 17, 2006 8:39 pm

So I am installing a switch like this right now. I starred up my van to check my new gauge cluster, and when I turned the key off, the van stayed on. DOOH! I am backfeeding the ignition switch. I wired basically per this last wiring diagram:

So I'm thinking the quickest fix for me is to install a diode on the swith to prevent it from backfeeding the ignition swith. Any thoughts?

Fri Aug 18, 2006 6:54 am

have only just begun reading, but it seems like the simplest thing to do is reconnect the yellow wire to the aux. batt. and then get a stereo that does not require the key to be on, or rig a switch to use it with the key off.

i think everythin but the starter/engine should run off the aux. batt. . that should eliminate the jumper cable situation every morning after camping with amenities(lights, heat, stereo, etc.).

that's the re-wire scenario i could use a little help with eventually.

Fri Aug 18, 2006 7:29 am

Yes, I have eveything run off the aux battery but the starter. The problem is that I used a SPST switch, when I really should have used a SPDT to prevent the auxiliary battery from backfeeding the ignition switch. Now the easisest fix for me I think is to install a diode in the wiring coming from the ignition switch. Here's what I was thinking:
http://www.radioshack.com/product/index.jsp?produc...age=search

Fri Aug 18, 2006 10:21 pm

I think Exitstrategy got it right.

Do what all boaters do......run everything off the house (aux) battery except the engine start.

On my EVC, the house battery is a huge group 31 deep discharge marine battery designed to be discharged heavily over and over. The only reason the radio and a couple of interior lights run off the starting battery is that Winnebago didn't want to fool with re-wiring the factory supplied van body.

Your starting battery will last much longer doing it's starting job only, and the house battery will last longer and give you better performance if it is a deep discharge type.

The downside is that you can leave the radio on by accident and run down the house battery, but it's going to take a long time if you have set things up the right way