Re: where's a good ground in back?
You could draw a ground cable parallel to the plus cable from the battery to the trunk.
I've done that in former times in a predecessor of my xf, because i've had big problems with hum and ground loops.
I know it's more expensive, but it's the safe way.
BTW: What is the exact problem? Maybe there are other causes.
Did you check the mass connection between battery and chassis?
Did you add a mass cable with the same diameter than you're using for plus between battery and chassis?
Last edited by bigblock427; Feb 28, 2011 at 04:40 PM.