speedometer and milometer not working

[cococola]

My 944s 1988 has an issue in that the speedometer and milometer are not working, I have stripped the speedometer down and the cogs are all in good order so I'm assuming that it is a fault with the speed sensor at the gearbox end?
I wonder if there is anything else that I may need to check and how I can check the speed sensor, additionally is the speed sensor a serviceable item or is it a replacement unit only?
many thanks

 

[bmnelsc]

Here is a link to a Rennlist discussion re the sender. Also should be described in the work shop manual which you can find online (usually).
https://rennlist.com/foru...er-impulse-sender.html