Hi all, well we are getting somewhere, yes I do believe its a w4a as I can see the what looks like a torque converter looking in the fins on the bell housing, went looking in all paper work I got with it years ago and it is built on a t1 409d chassis number starts with 611, went to my local merc dealer when they opened today but they only do cars now, but told me of a place to send photos to and they are going to get back to me tomorrow, tried one of them on line ask an expert, who said it my reversing(back-up) light senor but if plugged in or no lights work ok, waste of £27, right as promised going to try and put some photos of my beauty, if it fails my lad said he will help me tomorrow, dave