Try this,
1. Unhook everything
2. Ensure you slide the cable all the way into the back of speedo. Need to make sure cable is all the way in. Screw in tight.
3. Reconnect at transmission side. Ensure tight.

I know this sounds stupid. I actually took speedo out of dash to ensure I had it in all the way. If speedo works with drill and transmission is spinning the cable, it ican not be seated correctly. I had the same issue.

Chris