HEI Large /Small Cap - Tach Signal

When I hook the inductive clip on a plug wire I get an RPM reading on the Equus tach … when I hook up the tach lead up to the negative side of the coil I do not. I haven’t tried the tach on another vehicle so it may just be a faulty tach.

I’m not a fan of the inductive clip being seen but it has worked so far … I would just like to clean up the engine bay a bit.
Post a picture of this inductive tach.