Why has my tachometer/revs meter stopped working?

loose at either end or the cable was dry and snapped somewhere, take it off at the easiest location and it will pull free and you can inspect.. Don't let it fall in the dirt! You will see if it is broken, if not add a lil grease to each end and re-inster it carefully till it's seated then tighen up. If it's not a cable you prob have a loose wire in there, check ground wires that are black for loose connection