Hmm. Maybe the cable is the wrong type. My dad has 66 Mustang he's restoring and we pulled the cable out and tried it on his speedo since he had it removed from the cluster and it slipped right in and worked a peach. What I'm running into is they've changed out what I presume was a standard transmission to what I'm pretty sure is a 904 automatic transmission. Might be looking at a conversion issue with an incompatible cable to the speedometer.