knock sensor help

[adz_sportif_turbo]

well i done a diagnostics to find code 52,,,knock sensor. when i checked the wiring it had been cut by the previous owner. so i twisted the wire back together (just the inner wire not the shielding) and it done nothing. can anyone tell me how the shielding earths?? and is there any way i can test the knock sensor?? any ideas what my problem could be as im only boosting .5 bar so im guessing my timing isnt altering

thanks