Help needed, I am STUCK

I am trying to install my tach and I can not find the lower black wire on my ignition coil or my PCM, I have searched the net and can not find what I am looking for. (I am at my cousin's and we have had about 5p eople look at it and noone can seem to figure out where to hook the tach.) I am told the tach can be hooked to teither of these places. Please help ASAP! Time is a wasting away, and my car is in a few pieces!