Does anyone know about electronic 'noise' in car wiring?

Pondy

Muppet
 At the summit of the picturesque fens
Any vehicle electrical/ electronics experts on the forum?

I have an electronic speedo in my 'fauxrrari' which has suddenly decided to play up. It has been tested by the manufacturer and is fault free, so it isn't the instrument.

I am getting significant 'noise' or 'interference' from somewhere, which is confusing the speed signal wire and causing it to go haywire. It recorded a speed of 588 mph the other day, and I was in my cul-de-sac. :eek:
I am trying to find out where to start looking for issues.
For reference the speed signal comes from a speed sensor mounted in the diff. I am 99.9% sure that is OK, judging by the way the fault is showing.
The instrument worked fine when first installed and was OK until I parked the car up in the garage over the Winter. First outing last week and it started playing up. I have rewired the signal cable, re-earthed the sensor and checked for connection issues. None have been found so far.
 
Google ferrite beads …standard methodology for disrupting induced electrical noise..
I really need to find the source of the noise and why it is happening, cos it wasn't before.

It has been suggested that I run a new shielded cable from the sensor directly to the speedo input. That would rule out any issues with noise from the sensor cable.
 
I really need to find the source of the noise and why it is happening, cos it wasn't before.

It has been suggested that I run a new shielded cable from the sensor directly to the speedo input. That would rule out any issues with noise from the sensor cable.
Noise that suddenly appears is usually an earth fault…either a proper earth has disconnected or there’s a bogus earth appeared…ferrite bead is just a standard technique when it’s TFD
 
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