Abstract: Input current from the automobile lighting circuitry is conducted to movable poles on a first relay. Normally open contacts in the first relay are connected through output conductors to corresponding lighting circuits on the boat trailer. The first relay contacts close when operating voltage is applied to the first relay coil via a normally closed contact in a second relay. When a float switch on the trailer enters water, it closes, thereby actuating a transistor which, in turn, actuates the second relay. Upon actuation, the normally closed second relay contact opens, thereby deactivating the first relay and arresting current flow to the trailer. The transistor is maintained in an "ON" state for a period of time after the trailer emerges from water by current from a capacitor. The capacitor receives a charge via the second relay upon application of the automobile brake pedal only when the transistor is in the "ON" state.