(not so) new car stereo renders speedometer inoperable

[Tom_Jane]

I removed the good cd player from my Barina and put an old one in and immediately noticed that whenever I had a cd playing the speedometer did not function.
It just sat at zero and didn't move. As soon as I removed cd the speedo began to function again.

The car stalled also. Possibly unrelated. It does stall once every blue moon.

Anyone know what is the problem here?