My rev counter has suddenly stop working on my K reg 405 diesel, how do I
> get it to work again
Normally the sensor goes. It is only about £12 from the peugeot dealer, and it plugs into the gearbox bellhousing just where it bolts onto the engine, at the rear toward the top.
Hopefully there is more room around it in the 405 than the 205 which I had, because in that you had to go through all sorts of contortions to remove it.
It just pulls out (it's tight in a hole) and the new one pushes straight in.