i'm in the middle of re wiring some stuff behind the dash of my 82 f-150. i'm just looking to see if anyone knows how to wire up the factory tach, which came with no wiring harness to the engine which is a 351 m. i know how to hook up an aftermarket tach no problem, i just don't know which prong is for ground/positive/coil, if anyone to help me out on this it would be greatly appreciated