This is a frequent question asked by many customers looking to purchase head units from us and also customers who have purchased from us and been told that the stereo is draining their battery by a so-called 'professional'. So, we are here to give some guidance and put the mystery question to bed.

Although not many people like to hear the answer here, the only reason why you would suffer from battery drain after fitting a new after-market head unit is incorrect installation. It is as simple as that. There is absolutely no other reason for it. Any car audio expert or auto-electrician worth their salt will tell you this.

So, why will an after-market head unit drain a battery?

After-market head units are dual sourced, this means they require two +12v feeds and an earth in order to power. One of the +12v sources will be a direct battery feed, so it's reading +12v at all times. This is known as the battery backup. It's what essentially keeps the memory of the head unit. The other +12v feed will only come on when the keys are turned onto accessories, hence this wire is called "ACC". This means the +12v feed for this is only coming on with the ignition. 

Battery drain will happen if there is more than +12v source being received into the head unit when the keys are off. Remember there should only be one +12v source, the battery wire, when the keys are out. If there are any other cables receiving +12v when the keys are out, then this is why you are suffering from battery drain.

It is physically impossible for the head unit to produce it's own +12v feed. So, it will be an installation based issue. 

My fitter has said it's the head unit that is draining the battery?

OK, if someone says that, then they should be able to back this up with what cable and why. If they cannot, then they are simply making a guess. Any decent auto-electrician or audio specialist will be able to diagnose battery drain with the wire responsible and why it is causing the drain. Once they do that, they should be able to easily put it right.

So what could be causing the battery drain?

On a head units power loom, you will have the following power connections:

YELLOW Wire: +12v BATTERY (Constant)

RED Wire: +12v ACC (ignition based only) 

ORANGE Wire: +12v ILLUMINATION (ignition based only)

BLUE Wire:  +12v REMOTE AERIAL AMP (ignition based only)

BLACK Wire: Ground Earth

You see that only one wire should be +12v at all times. So if any of the other wires (red, orange or blue) are receiving a constant +12v feed then that is going to be the reason why you are suffering from battery drain. All you need is a multi-meter and you can test all of these wires. You would easily identify which cable is receiving the the wrong feed.

How to resolve?

If one of the wires which should be ignition based are reading as a constant feed then all you have to do is move the wire to an ignition based feed. Simple.

But the stereo I purchased from you was listed as being plug and play?

Yes, our vehicle specific head units are plug and play but most of them are able to simply adjust between canbus and non-canbus applications. It's important that you have yours set up correct for your vehicle. Incorrectly setting them up may connect the ACC cable and give you that unwanted second +12v constant connection, which will cause battery drain. 

We can always advise how to set up correctly if required.