I am going to replace gas cooker with electric,what do I need to disconnect the gas cooker and to reconnect the electric, there is an electric cable with grey box attached to it already in place at the back of the cooker ,there used to be a switch that I could put up or down on the wall beside cooker but tiled years back not sure where it went maybe behind tile, do I need this switch or can I put grey cable straight into cooker.