Proper ground for Aux In Input/12V adapter

[pierremcalpine]

I'm currently using a device that plugs into the back of the stereo CD changer port for my aux in input. This works great except that now that I've switched from a blackberry to an iphone I'm getting increased interference any time I plug my 12V charger into the charging port.

I'm pretty sure this is due to two different grounds being used (the aux in device grounds onto the frame of the stereo and the 12V charger is grounded via the 12V plug) so I would like to take the ground for the aux in device and re-route it to the 12V input instead. I've gained access to the underside of the cigarette lighter and have unplugged it and there are three wires going into it: a thick one (12V feed I'm presuming) and two thinner wires. One of the two (thin) wires hooks up to the sides of the cigarette lighter (neutral???) and the third well...I think the third is ground...It's a stupid question, but is that right? Is there a typical colour for ground? I think the two thin wires are green and brown with the middle one being black...?

[v40alex]

Isn't one of the wires the feed for the built in bulb? The earth will be the one on the side of the metal.

[pierremcalpine]

Seems to have worked, no more loud humming while one a phone call or while listening to music on i-phone when phone is charging. I ended up splicing into the wire that had connectivity with the side of the 12V adapter (ground) and stringing it back behind the front console and then tucking in under one of the stereo cover bolts. All good. Stereo and 12V now have a shared ground.

[pierremcalpine]

Update: did not work. I did a bit more research and it turns out that all I needed a "ground loop isolator" put in between the phone and the device that plugs into the cd changer port. $10 later absolute silence when charging. Very cool! You can find these easily enough on amazon. NOW I'm good.