I think you'll find that what has gone wrong there is the 'magic smoke' has escaped from the speedo.
As most people know there is 'magic smoke' inside all electronic components which allows them to work. Once the smoke has escaped they cease to be. However, at this point they can make very good little silicon heaters (as shown above).
Here endeth the first electronics lesson, next time I'll explain where the mirrors come into it!
G