OK thanks for the leads. How do I check the coax? it is all sealed up with coating from one end to the other? Put a small hole in the sheath?
Also, meter the connectors at the cig lighter when the bike is on run. You may also want to sandpaper the spade connectors in case there's some oxidation built up on them.
What headlights are you using? I know some LEDs have been causing interference for guys. Is there any other electronic devices that turn on with the ignition, but don't when you switch to aux? Just spit balling here.