1982 GL1100 weak spark on #2 and #4?

I've changed all spark pug wiresI've checked spark unit by reversing connectors, still intermittant spark on #4 .I've checked manufacturer's specs on pulse generator ohms (530 ohms), reads perfect.The strange thing is that if I unplug all spark plug wires from the spark plugs, there is no spark at any spark plug wires.If I connect all spark plug wires and remove one at a time, then #1 has good spark (disconnected), #2 has no spark (disconnected) , #3 has good spark (disconnected), #4 has intermittent spark (disconnected).If I remove #2 when the bike is running, then the bike dies. But when I check #2 for spark with the wire off the plug, there's no spark.Is this a bad ground?