1. Remove loose rust with a wire brush or high pressure water.
2. Apply a liberal coat of Corroseal Rust Converter. Will convert rust to an inert material and prime in one application. Cleans up with water
3. Apply a good quality topcoat paint
For added protection of electrical connections, a liberal spray of CorrosionX on all electrical connectors, the bulb holder and any exposed metal will give many months of corrosion protection.