Car: E60, 525d Dec 2007.

I have a problem with the signal on my GPS. It works mostly ok, but in weak signal areas, wanders off the road I'm on.

I have installed cameras in the front and reat of my car, long story, anyway, the camera in the front is attached to the support for the driving mirror. No interferrence. I put a switch in the plastic with the hands free mic, airbag warning etc, and ran power from the switched green/white wire in the boot to it. I ran another cable back from the roof switch, inside the roof, to the drivers side passengers handle and down, behind th erear seats, and back to the boot, where the camera power socket is.

Originally I ran the back camera's power along the roof to the roof brake light, down the rear passengers side pillar, and on to the camera. I changed this, as with the rear camea on, there was interference on the radio and GPS traffic failed.

My question is, where does the GPS/ Radio aerial cable run? I want to make sure that I've avoided it, and check I haven't damaged it while running the cables. I've put ferrite cores on the cable running to the rear camera, and it's power wire.

Any help would be apprechiated.