Speed signal on a 2003 A Class

[marnix]

Hi
I have just fitted an APS 30(4716) navigation system to my wife's 2003 A160, but it does not seem to reconise the fact that I'm moving. It shows my initial position but does not update the directions as I move along.
I've tried the system in my SLK and it works perfectly (Just to prove that the unit is not faulty).
I have a wire connected to A1 (speed sensor) on the back of the unit but I wonder if the other end of it is connected?
Can anybody advise where I can found the speed signal. Is it in the passanger foot well as on the C and E class models. Or do I need to trace it all the way back to the ABS system at the rear wheel?
Any advice is mostly welcome.
Thanks

 

[marnix]

I sorted it out.
Broken speed signal wire at the back of the socket.

 

[pascal]

Was wondering how you could have a wire to A1 coming from no-where.