by a transistor q 6 q 8 q 10 and q 12 respectively which are in turn controlled by a common signal from the microcontroller 20 u 8 the current flow path through each led bank 26 passes through the input and output of the voltage regulator u 1 u 2 u 3 u 4 a 4 resistor network and the darlington pair transistor q 1 q 2 q 3 q 4 to ground bank sense circuits 28 employ transistors q 5 q 7 q 9 and q 11 to sense current flow in the current flow path and provide a fault indication to microcontroller 20 u 8 in the absence of current flow through an led bank it will be understood that failure of an led in the series of leds of an led bank will result in an open circuit and the current flow through the bank having a failed led will drop to zero in the illustrated circuit a logic level high at microcontroller inputs rc 0 rc 1 rc 2 and rc 3 indicates normal functioning of led banks b 1 through b 4 absence of current flow through the 4 resistor network of a respective bank driver will.