Liquid level tamper alarm

In a vehicle having a liquid fuel tank containing a variable resistance depth gauge transducer, an electric fuel gauge, an ignition switch, an electric traffic warning horn, and a battery, said transducer, fuel gauge and ignition switch being connected in series circuit across said battery;

• the improvement comprising a fixed resistance and an adjustable resistance connected in series between a terminal of said transducer which is connected to one terminal of said battery and a terminal of said fuel gauge which is connected to said ignition switch, a relay having one terminal connected between said fixed and adjustable resistances and another terminal connected between said transducer and fuel gauge to form a bridge circuit which may be balanced by said adjustable resistance at any existing quiescent fuel level to maintain said relay normally deenergized and wherein any upward or downward movement of the fuel level will change the resistance of said transducer to unbalance said bridge circuit and energize said relay, and circuit means operable by energization of said relay to sound said horn, a signal lamp arranged to indicate a balanced or unbalanced condition of said bridge circuit;
• said circuit means comprising a relay switch which is closed by energization of said relay, and a three position manual switch, said manual switch having an open position disconnecting both said horn and said signal lamp to prevent the energization thereof, said manual switch having a first closed position connecting said signal lamp in series with said relay switch to energize said lamp when said relay switch is closed, and said manual switch having a second closed position connecting said horn in series with said relay switch to energize said horn when said relay switch is closed.