Yayy! fixed it!!
After a diligent search i finally found the fault. it turned out to be one of the earth wires coming from the multiway connector had a break in the insulation and was picking up a live feed from somewhere. a bit of dampness and a recipe for problems. the break was almost inside the connector and very easy to miss, and as i wiggled it the wire broke. so i just ran it to a clean earth point on the body and everything worked fine!!
Thanks for all the suggestions guys.
Snowy.