Dont know for sure but if you ground the negative side of the coil I suspect that you will not produce a spark. On a standard point ignition the negative side of the coil goes through the points to make and break the ground thus producing a spark. if you grounded the negative side there would not be an opening of the ground to the coil to allow the coil to spark. My guess is that the HEI type of coil works the same way and the pickup in the dist simply makes or brakes the negative side of the coil.
