h.e.i. tach problem

[thisolechevy]

I coverted from points to h.e.i. a couple of months and personally I beleive that it is the best thing since sliced bread...lol anyways my tachometer (which I know is good because it has a shift light and I can still set the shift rpm so I now its functioning correctly) the tach wont work, I know for a fact that all wires are good and ran correctly and all fuses are good and that sort of thing, is there any way some part of my dizzy is bad? I had tach w/points and no tach w/hei (the tach is hei compatable)is there some type of selinoid in the dizzy for this?