I have a '99 Passat and I'm trying to fit up a new stereo.

The old one is a Sony after market job and had some kind of ISO -> Sony adapter plugged in. The new one takes ISO connectors straight off, which seems to be a massive ball ache due to my dodgey wiring.

So far using a multi-meter I've worked out that my car's permanent power and ignition power are reversed (Turning ignition off was still providing a low current, enough to make the new stereo try to start up but fail), so I've reversed those two wires and that seems OK.

Now the problem is that when I turn the ignition off, the stereo says "Goodbye" and shuts down, but there's a back light behind the volume knob and the phone control buttons that stays on. It's very dim, but definitely on. There is also a seemingly random and variable hiss to squeal through the speakers with the ignition off. Not loud, but definitely there.

The new stereo is a noname brand, a Mutant MT7609BT by armour automotive. I've emailed their tech support place that confirms that the knob back light is definitely meant to go off. Given the frankly atrocious wiring in my car I'm inclined to think the problem is on my side, and not the new stereo. Anyone got any ideas?

The cars permanent power tends to be a direct line to the battery which should power the stereo without any issues so it sounds like that low current supply is something else.

Sometimes you have wires for ignition, battery (which is often fused) and then sometimes lights if that is provided where a backlight may come on when the headlights are on, but I don't know if that's so common these days.

Any idea where that low powered wire comes from?

I'm assuming it's low power (hence the thing trying to start up but not managing). I haven't checked the current on it yet.

My ISO A connector has a bunch of other leads on it that my stereo doesn't need - at least one of which was providing 3 or 4 volts with the ignition off - can't remember which, but perhaps that was the illumination line? I can cut the fucker off it it's the source of the problem.

The low power wire comes from the big spool of wires behind the dashboard :|

What colour is it?

I think nearly every time I've helped someone pur a car stereo in the power cables have been the wrong way round. Normally you'd have two fatter cables, one 12V permanent and one 12V that is switched with the ignition.

Can't recall exactly, either red or blue & red.

Aye, that was the initial problem. They're then correct way round now but still getting odd behaviour. Disconnecting permanent power means nothing works at all, even with the ignition on.

What happens if you swap them around? Does it stay on all the time?

Some stereos will take a feed from the light switch to change the display brightness at night. However, to be honest, it sounds like you have an actual issue with your wiring - all vehicle electrics should be at ~12-14 volts, anything less indicates a problem with voltage drop. Often a bad ground, a bad contact or even a short.

Remember, also, that current isn't restricted normally - the device will pull whatever power it needs, and if the wiring is designed for low current, then there should be a lower rated fuse to blow. As you're not blowing fuses, it sounds like a voltage problem.

It tries to stay on but doesn't seem to have enough juice yo boot up (perhaps because it needs both pins to have power? I dunno)

It tries to stay on but doesn't seem to have enough juice yo boot up (perhaps because it needs both pins to have power? I dunno)

Your permanent should definitely power it just fine. As Dan said, sounds like a few issues with wiring. Or some odd extra wires that the car provides that aren't needed.

Have you checked the two main power lines are 12V?

Think I've fixed it. There was a permanent 12v coming in from the antenna motor pin. That's supposed to be an output pin from the radio to the antenna motor so was probably playing merry hell with the circuit. Snipped the wire and seems to be working correctly now.

Yeah, I can't imagine that was doing you any favours.

Your welcome.

What about my welcome ect

Maybe you forgot to plug it in.

I think I need to up the agp voltage.