that the push rod 14 has traveled sufficiently to close the first pair of contacts 31 a red light emitting diode 64 indicates that the push rod 14 has traveled sufficiently to close the second pair of contacts 32 each shift register 63 is shown having associated therewith eight light emitting diodes of a single color the color reflecting the extent of push rod 14 travel for each of the eight brakes on each side of the vehicle as well known in the art the location of the first pair of contacts 31 and the second pair of contacts 32 can be selected in such manner that closing the first pair of contacts 31 serves as a warning to the operator of the vehicle of wear of the brakes and that closing the second pair of contacts 32 serves as a warning to the operator of the vehicle that the brakes are dangerously maladjusted and in need of adjustment with continued reference to fig1 there is shown an alarm circuit comprising a transistor q biased by resistors r1 and r2 for energizing relay k upon the occurrence of the closing of any of the second contact pairs 32 the microprocessor 60 generates an alarm signal which turns on the transistor q thereby closing contact arm 67 a voltage source is thereby connected to a buzzer 69 and a warning light 68 the buzzer 69 and warning light 68 preferably being disposed in the cab of the vehicle to alert the operator of the vehicle additionally for vehicles so equipped the same alarm signal can serve as a speed control signal to a vehicle engine speed control means 71 to slow the vehicle so that the operator can make.