I went out and looked at our 107. There are 2 visible wires in the arch. One is in flexi tubing and seems to go towards the number plate lights. The other seems to head towards the centre of the wheel hub. I've checked in my Haynes, but it didn't help. Could it be something to do with ABS or brake shoe warning? You should maybe take the wheel off and see if the wire will locate somewhere around the hub. Good luck.