Mercury - 10-Pin Weather Cap Harness Port Protection 888507T. Overview. Unused harness ports can collect moisture and grime faster than most people realize, especially around the transom or rigging bay. The Mercury 888507T 10-Pin Weather Cap closes off those open connections and keeps the electrical system cleaner over the long run. With a built-in mounting tab, it stays secure and out of the way, giving any exposed 10-pin plug point the protection it needs in a wet, high-vibration environment..