Hi, I'm try to find out why I have no spark on bottom cylinder. It's not the coil. it tests good. What is the test for the cd box to determine if it's OK? The manual I have is a 1991 . All it coves is the mercury ignition system, so I'm stuck trying to trouble shoot the presto lite system I have a dva meter but not sure how to hook it up on this blue stuff. Compression is an even 125 psi on all cylinders. Thanks......Robert