The speedo on this fluctuates even when the car is not moving,anything between 10 and 50 mph(worse with engine running)The vehicle has previously had new gearbox speed sensor and dash pod by main dealer.Scope the speed signal wire and you can see a random square wave produced both at dash and sensor connector (disconnected).Main dealer has quoted £3k to fix it with a new wiring loom!!!.It possibly may have a fault in the loom but where is it picking up this pulse from?Any thoughts?