This may not be as easy as it seems.You could use a pod out of a car with a rev counter and you could be lucky and find it already wired in connector plug.(doubtful).The alternative would be to wire the speed impulse wire to the alternator .Some units are fitted with a "w" terminal connector that gives a suitable output for a rev counter.If this is not avaiable it would need a wire soldered inside the alternator.hth