Hi my name is David and I am having some issue with installing an aftermarket tach on my 5.0. I have it all wired and eveerything is correct but the green tach wire. I have tried hoking it up to the negative side of the coil and everywhere on my distributor. I have a few posts but know one can seem to help. Any help would be greatly appreciated. I think I may need to buy the hei wiring harness but not sure as I do not have a msd ignition box. Only a msd distributor and blaster coil. When I hook up to the negative side of the coil it is giving off current. I am lost........