Abstract: A signal light system is provided for vehicles to indicate the operative condition of the vehicle to another motorist. The signal light system is responsive to acceleration and deceleration of the vehicle in addition to actuation of the braking mechanism in selectively responsive energization of respective indicator lights for each of the three conditions. An electronic control circuit uniquely capable of providing error-free signals responds to a signal input from the brake mechanism for primary control and secondarily responds to actuation of the accelerator pedal for indicating acceleration or deceleration of the vehicle. A pressure responsive switch mechanism is provided for assembly with the accelerator pedal and is the condition-responsive element capable of producing an input signal that effectively eliminates the possibility of generation of error signals by the control circuit.