Taking Planenuts thread drift a smidge further .... My normally sensible speedo started doing silly things , reading true speed then randomly shooting up to max speed then min speed etc. Turned out to be a corroded connector in the totaly exposed electrical connector by the speed sensor on the front offside wheel ( UK ). This was causing false readings. Fix was to strip off the old connector and fit new, except with weathproof rubber boot to make it waterproof.
