I used spray brake parts cleaner from Walmart as contact cleaner for years, but it may be too strong for what you are wanting it for. You can get real contact cleaner at NAPA. Not cheap. I would first try WD-40 if you haven't already. It is a fairly decent solvent for cleaning handlebar switches, and will not harm plastic. It also leaves a protective coating to help prevent corrosion. If that doesn't work, you can still try the contact cleaner.