Hi Dave, If it is a loose wire, the first place to start is in the spare wheel well, remove the black plastic trim to reveal the two boxes that help make up the sat nav components.
It's the unit on the right you need to check, that's the radio tuner. Is it wet down there? are there any signs of rust or corrosion?
Lift the radio tuner up & out of it's metal casing. I would suggest re-seating the 17 pin multipin plug on it, to see if it makes a good connection again.
To do this, you need a flat bladed screwdriver. Gentling push the end into the black plastic clamp that holds the connector on, you'll see a little indentation showing where to put it.
Once you've prized it up it will then be free for you to pull off (but be warned it is a little stiff.)
Once off, lift the little blue horse shoe shaped clamping pin out which will release the additional two mini connectors, these are for the CD and Tape unit.
Put them back in again, and clamp shut with the blue pin, then offer up the 17 pin plug back to the radio tuner and snap shut by pushing forward & down.
This may well remake a good connection.
Let us know if it doesn't work, and we can try something else.
BTW, I've merged this thread with your original one to keep them together, and moved it to the I.C.E Forum.