have a problem with my tach

[ksdmed]

Okay, here is the problem, I have an 89 coupay with an SR20DET swap and the tach does not work. I replaced the tack from the SOHC with an SR tach but still no workie. I have read fourms and searched differnt fourms for an answer. I do not ask many questions, much rather find the answers myself but I am lost here. What I have read is just swap the tach and it should work. I did take the face of the SOHC and put it on the SR tach, I have a HUD cluster.