Toran

Hello All,

I have plans for moving the stereo completely to an auxiliary battery located in the rear.
The stereo's yellow wire(constant 12v) is connected to the auxiliary battery's positive terminal which allows the radio to be on without key. How would I wire the stereo to the auxiliary battery so that the stereo turns off when the key is out?

Would I need a relay?
Break it down for me please good people

T.I.A.

FrenchToast

Um. How much current does this stereo draw?

All I can tell you is ignition is green (solid) in terms of wiring.

Edit: rather than give you unconfirmed wiring advice, I'll let someone else speak.

Take care!

Toran

The whole stereo setup is about 75amps.

Van

Well, presumably you'll have some sort of relay/switch system for charging your axillary battery from the alternator - use that circuit for the yellow wire. When the engine's running, the yellow wire will have power; when it's not, it won't.

Toran

I have a battery isolator so that the auxiliary battery can receive a charge.
Also there is a 12V 40A relay I had in a drawer.

Van: So your saying to simply connect the yellow constant power directly to the isolator?

Cyberpunky

Dual Battery set ups are best avoided IMO unless it is a show car, and even then I would use a power supply. You have several methods to connect a 2nd battery and depending on what you require the 2nd battery for, then that would determine what method is best. Dual battery set ups can easily end up adding another hole in your wallet, and as you already have a 944 do you really need another drain on your funds ?

It sounds like you are not wanting a 2nd battery for engine off listening, so your best bet would be a higher output alternator, that has high current at low rpm. Your system runs off the alternator when the car is running, not the battery and a 2nd battery just adds another load to the alt, leaving less current for the system.

My advice would be to upgrade your alternator and fit a bigger AGM battery and forget using a 2nd battery.

Anyway the simple answer is to run the red (SW) wire to the ignition, but this is assuming the 2nd battery is hooked up to the primary battery when ign is on
peace
Cyberpunky

Toran

Thanks Cyberpunky.
The 944 is indeed a fund drainer!
I got the auxiliary battery along with the isolator and wiring nearly a year ago and want to properly set it up at last. Since I already have it might as well install in.

Cyberpunky

why ? what are you hoping it will do ?

Toran

It's a two part interest.
1st: Move the aftermarket accessories to the auxiliary battery to ensure primary battery strength for cranking.

2nd: Have the auxiliary battery run a few camping accessories when out in the wild.

I have fresh alternator brushes and a new voltage regulator.
I do think for awhile there had been a power drain between the car alarm and aftermarket stereo gear.

V2Rocket

If you go to the boneyard and look for Ford Contours they have a few 70A relays in their fuse box. One is for the fan (green), one is something I don't remember (black relay). I got a few for $2 each.

Your wording is confusing though. You want to wire it so that it doesn't need a key, but then will shut off when the key is out...do you mean auto shutoff when you turn off the car, but you can turn it on whenever?

Toran

V2Rocket_aka944 for now I simply want to have the stereo be powered by the auxiliary battery & turn off when the car is off(key removed).

How would I wire this 70A relay?

UltimatE157

This is much simpler than you think.

Hook all of your power/ground heavy gauge wires to the aux battery. Hook everything up normally as you would in a normal install (Remote wires from the amps to the head unit). Then just take the head unit's 12v+ switched wire and put it to the car's regular 12v+ switched radio wire, or any 12v+ switched wire in the harness.

Now when you turn off the car, the harness with shut off the radio and the radio will shut off the amps. I would absolutely avoid using 70A relays to switch high-current wires. Don't forget to run proper fuses on the power wires.

That being said... I would go the single high quality battery with a high output alternator vs. a dual battery setup.

Jamesr6967

For the camping idea, it is a good plan to have dual batteries. I have done that with my 4X4s, and it saved my butt in the 'boonies' numerous times, especially if you use a 12 volt cooler. Use the later 944 alternator as it puts out more amperage, or get a shop to rewind yours to put out more power.

Cyberpunky

This is the ideal use for dual batteries and is best done with a device like this Click Here. Going dual batteries for car audio is less than ideal and method of connection/dissimilar battery type/vampiring etc are the complex reasons why not to do it(too many issues to go into here).


Going first option is a good idea but 2nd(rewind) option isn't(usually).

When you rewire an Alt you actually lower its near idle output, and so it will produce less current at low RPM(often from 9 amps down to 2-3amps) and only puts out higher output, at high rpm(can be ok if all driving is at highway speeds). In car audio applications we want high current at low rpm as well as high, and so a rewound alt isn't usually the answer. A better option is what emergency vehicles(cop/ambo/etc) use and that is an alt that has high output at near idle.

An ambulance(ambo in aussie parlance) needs to keep its medical devices running even when stopped at a light etc, so uses an alt that puts out around 60 amps at near idle, and about 160 amp at high rpm. Bosch make one that locally is known as a cop/ambo spec unit. I use a slightly lower spec unit in my old car audio competition car that puts out 40 amp at near idle and 120(ish) amps at higher rpm, which was all I needed in my 40+ year old car(it came stock with a 15 amp alt).

Anyway I used rewound alts and went through about 7 or 8 optima and stinger batteries (@ $AUS400 each) before I got a decent alt and an education in dual batts and got my system right. It is amazing the amount of incorrect info around about dual batteries and how to set them up, and also about alternators
good luck with your set up whatever you decide
peace
Cyberpunky