Speedometer Help

I have a 72 duster with a factory speedometer unit. It is not working and I cannot figure out why. I purchase a new cable like the one pictured below. Installed it making sure that the little clip fits into the grove on the speedometer unit....no luck. I tried another speedometer unit...no luck.

In both cases, i checked the connection to the transmission to make sure it was tight. I tried wiggling the cable while driving ...no luck..the speedometer needle does not move at all.

Any suggestions...anybody? What do i try next?