How much money do you have : ), Just kidding.
You said the red wire ground on the engine case is fastened securely, correct? Spray some electrical contact cleaner on it just to make sure it isn't corroded.
Are you referring to light switch on the handle bar? Some Ciaos also had a combo light/ignition switch on top of the headlight case.
If it is the handle bar switch have you taken it apart to check for loose wires in the switch? There are tiny little screws in the switch terminal block that hold the wires in place. Check all these to make sure a wire hasn't slipped out.
You can use some electrical contact spray to clean the wire ends and contact points. If you loosen those screws make sure they don't fall out because you may not ever find them.
When I work on the switch on the bike I hang a plastic bucket over the handle bar so it is under the switch. If I drop anything, it falls in the bucket.
You may have to replace the switch but try cleaning all the contact points first and cleaning and reseating the wires.
If it works you can send me a Million bucks.