RE: spark plug cap replacement
With the CM-6 plug there is a resistor in the cap and the end of the resistor goes into the spring
The lead wire is protruding at least half way into the spark plug area of the boot and goes between the coils of the spring
When the plug is inserted, it compresses the coils of the spring against the wire.
The caps using resistor plugs are made different and do not have a resistor in them. I don't have any RCEXL caps using like the NGK BPMR6F resistor plug. Mine are all rubber CH.