external aerial for navigator bluetooth??

I've got a Navigator 5.00 with bluetooth, but my car has electrical elements front and back. Not much signal from the side windows either. Has anyone worked out how to fit an external aerial?

I have just bough the same. Various web sites are offering external antenaes for bluetooth GPS but I suspect that old receivers had a specific socket whereas the new SirfIII receiver does not. No mention on the TomTom site either.

I too will be interested in replies / solutions