hi, my electronic speedo stopped working a while back, just went haywire and then nothing, at the speedo itself i've got power/earth/dash light and sensor wire going in, all ok except sensor wire, question is how do i test that wire? been told a circuit test wont do it.

I'd suspect the sensor and it's wiring then

You can check for continuity between the sensor signal and where that wire attaches to the dial. The only real way of testing for a signal is with an oscilloscope. The speedo sensors often have coils in them that don't like being clouted, if the trigger wheel or magnets have been making contact with the sensor they fail... A loose connection could also do this (the vibrating wire would initially cause a haywire signal as you describe).

it depens on the type of sensor tought...

if its a reed sensor it will work when you put it close to a magnet (stays open/clos)
if its with coils its hard to test it.

if its inductive you can test it stationairy..

Tks

thanks guys
looks like a new sender then, the only
problem the is how to stop vibration?
I had sender mounted on chassis picking up signal from propshaft bolts, cap head so distance was uniform, Sierra diff also mounted in chassis !
I had thought it had been hit by bolts, perhaps just grazed and damaged it. basically more outlay!!