This rubber gasket seals the gap between the rear lamp housing and the rear fender of the host tractor. It prevents moisture and debris from entering the lamp cavity, which protects the electrical contacts and bulb holder from corrosion. A degraded or missing gasket allows water ingress that leads to intermittent lamp failure or terminal corrosion. The gasket compresses evenly when the housing is fastened, maintaining a consistent seal across the mounting surface. On reinstall, clean the fender contact area and ensure the gasket sits flat before tightening the housing screws.