Speedometer Trouble

Oops, I didn't mean that the 150 speedo is of unknown origin, I meant that it's operating condition is unknown. It came from a cluster from a 67 or 68 Cuda, as the speedometer cable screws on instead of the later clip on style. I bought the cluster from the WPC swap meet in Warren, Mi. last year and the seller was selling it for a friend so he could not verify that any of the guages or the speedo worked. Turned out the tach from that same cluster didn't work either, but I fixed that. I will take Doktor X's advise and blow the back with a light blast of air and hook it back up to see if that changes it's attitude though!!! Thanks for any and all replies, Geof