Unknown speed sensor part
 

So while searching for a mystery rattling sound underneath my dash I spotted a part I didn't recognize connected in-line with my speedometer cable. Nothing is wrong with it (hopefully), curiosity has the best of me and I'd like to know what exactly it is. The part reads 59D-02578. Every search I have made turns up results in different languages. Even when translated they don't give any useful information. Anyone have any input as to what exactly this thing is? 1988 Cherokee Laredo.
https://cimg9.ibsrv.net/gimg/www.che...1cefb7ff68.jpg
Pic I pulled from the google

I've seen something like that on some after market cruise controls , and maybe on some factory cruise controls ,