<VV> Heathkit CO 1015 Ignition Analyzer

[Padgett]

And I thought the user's manual was under the unit but was rong so may take 
a dig to find. Remembered most of it but the probe has me puzzled. 
Obviously the red connection goes on the negative post of the coil since it 
triggers the tach reading and the black goes to ground but there are two 
inductive connections, a black blocky one that snaps over a wire and a 
longer silver alligator-type one that is definately designed to go over a 
plug wire.

The silver one seems to trigger the display. Where does the black one go 
and what does it do ? Surely someone in this group has one.
http://padgett.ws/files/probes.jpg

Padgett