How hard? I assume the cable screws on to the speedo (I hope it's not broken) but on the wheel, how hard is it to install?
You just have to remove the screw pointed to in the picture. Then remove the old cable and plug in the new one. Very easy.
(http://www.stat.unc.edu/students/trovero/photos/bike/speedo.jpg)
Cool. Looks easy enough. tomorrow I'll buy the cable and give it a fix-up.