I have just purchased a secondhand witter towbar & electrics. I have downloaded fitting instructions from Witter for the towbar but need help with electrics which have a relay/unit of some sort which has SB2 from rydertowing on the case. plus the plug with the wires cut off. I can map the wires to the plug pins but how do I connect it all to the car? Is there a halfwits guide somewhere ? Any help appreciated. Chris