Speedometer on horse lorry

[Steeleydan]

Today my sister and I went to fill the horse box up with diesal on the way to the petrol station the needle on the speedo was working fine and we could see exactly how fast we were going. Switched lorry off filled up with diesal, started up to come home and the needle on the speedo is on 0 and isnt showing us how fast we are going, but milage counter is still going round and the little red tacho light is still on, so we cant understand why the speedo needle is staying at 0. Any ideas or suggestions would be greatly accepted.

 

[Madam_max]

Mine used to do this. I had to lock and unlock the tacho

 

[bevcatt]

Not sure how to fix it but it is not a legal requirement as our lorry has passed its plating twice with one that does the same as yours .Just have to be careful through the speed cameras etc .