Speedo gone wrong?

[Welly Jen]

2 hours ago, AndrewBClarke said:

According to an aironautic engineer, a poor earth connection would cause the reading to go down to zero as a circuit would be broken. If the needle or reading goes up it is either a faulty gauge, sender or moisture.  I am going with the moisture problem to start with as it is the easiest (and cheapest) to resolve. I have used the car all winter so no idea why it should happen now. Not bothered about the mileometer but thought it might help with diagnosis. Roll on the warmer weather and we will see what happens!

This is what I found on my car when the earth to the speedo was accidentally left loose. The poor earth was allowing electrical noise in to the inductive pick up sensor wires perhaps. The earth also grounds the shield on the pick up wires. The needle would jump from the indicated speed to a much higher one, then drop to zero after a bit, then reset.

Jen