Engine check light and bouncing speedo needle!

I've had what I thought was two separate issues but it turns out they were the same issue. I won't lay claim to repairing this myself, we have electronic whizzkids at work who kindly found and sorted this issue.

Upon checking the ECU fault code it came up as speed sensor fault. After going through the wiring diagrams he discovered that the speed signal is taken off the back of the speedo. He stripped the speedo and discovered that the cup that the speedo cable slots into has four magnets contained somehow within it and the signal goes through a read switch. The switch was sticking and was misaligned so once he sorted that he put it back together and the ECU checklight is now gone and it has also fixed the bouncing speedo needle!

Incidentally to make ECU code reading easier he found the ECU fault cable that goes from the ECU and t'eed into it at source so I now have a small wire with a spade connecter on the end on the passenger side that I just have to ground to read the faults should there be any.

Just thought it might be worth cataloguing on here in case anyone has this issue in the future.

I have sold at least half a dozen speedo heads because of the same or similar problem. Vehicle will run fine up to about 40mph to 45mph then you lose all power and no throttle response.
{ This has been covered on here a few times now but for all our Newbies it's worth remembering.}
But the engine will sit there ticking over for a couple of minutes until the ECU resets and away you go again.
Until you exceed 45mph for a mile or so.

I have had garages phone me with that problem and one in Southampton just wouldn't believe me so I said I would send him the speedo for £25 but without charging him.
But when you fit it and find out that I am right you will owe me £35.
I was obviously right and he was very happy to pay £35.
But I only charged him £25 - - too soft!!