Here is a diagram
The only wire coming out of the ignition coil is the white wire going to the instrument cluster. All other wires are going into the coil. If you mean the ground signal wire, it will be the only one not labeled in the diagram coming from the distributor. You will just have to use process of elimination. Not pink not the other pink, not white or the other white, but the only wire left.
The wire you are looking for is the white white going from the coil to the distributor. It's called the pulse wire or the tach wire. The white one going to the dash is the same circuit and probably for a tach.
The one the other expert referred to that wasn't labeled was the high tension coil wire, not what your looking for.