knock sensor wiring, 3rd cable to nothing?

[loggyboy]

I have a fault on my 172, Occasionally doesn't start, fault code reader shows knock sensor wiring fault. Ive replaced the sensor but to no avail. The plug is 2 pin but there is a 3rd wire that doesn't go anywhere under a sheaf of insulation. The wiring diagram appears to show something wrapped around the 2 cables. Should there be something at the end of the 3rd wire?

 

[Imed ab]

Did get it causr i have the samr problem

 

[DamienW]

Did get it causr i have the samr problem

Anybody know the purpose of this third uninsulated wire? Should it connect somewhere? To earth maybe? Here's a picture of mine hanging loose

 

[Mavez]

Shielding wire