Speedometer Cable

So I bought this 1981 VW pickup, which a friend converted - he replaced the gas engine with a diesel (yes it runs on waste vegetable oil). During the process he removed the speedo cable. When we put it back in, it didn’t work because the plastic part that goes around the end of the cable was missing. We found that and put it in, but it still doesn’t work.

The gear on the plastic piece doesn’t seem to connect with anything - is there something missing?

By the way - the original gearbox was a 5 speed, now it is a 4 speed.