Definitely a ground issue. All the electrical problems on my 9660STS have every time been solved by discovering another poor ground connection, somewhere. And I've had the exact same issue with the lights cutting out the separator.
My most recent issue was due to corrosion inside the crimped terminal of a ground wire. Remove all ground wires and clean the terminals as well as the spot on the body where they attach to. Also pull firmly on all wires and see if one or more isn't worn by corrosion inside the terminal.