[Healeys] electrical problem

[James Shope]

this is a new one for me.  driving tri-carb about 30 miles from homedrome and
it starts to run erractic and finally quits.  lots of trouble shooting finally
pinpoints area of problem to top of dist cap and rotor.  no spark to plugs,
however, big time spark with cap off.  rotor is sound but no spark through
rotor, yet when rotor held with pliers inside cap, spark goes to any contact
selected and that cylinder will actually fire.  cap back on, no spark to
plugs.   have spare cap and wires to try tomorrow(had to abandon car at
daughter's house).  any ideas of the problem?   healeymanjim