5 75 volts provided to its emitter and through the resistor divider network on its base and turns on to switch on the red led 38 located at the status indicator unit 22 to indicate that there is an overflow condition for this particular cartridge housing 10 preferably resistor r 4 is 3 3k ohms and resistor r 3 is 1k ohms resistors r 3 and r 4 act as a voltage divider but also provide proper biasing for the transistor q 1 to turn it on the voltage at the junction of resistors r 3 and r 4 is lower than that required to turn on the yellow led 40 and the green led 42 or to drive the pump 12 thus the green pumping led 42 and the yellow system function led 40 remain off and no further ink is supplied to the reservoir 14 of the particular cartridge housing 10 when in the overflow mode however the red led 38 illuminates to indicate an overflow condition to the operator when the overflow condition is corrected the safety overflow level sensing switch 18 will again close i e its normal conductive condition and normal operation of the pump circuit will resume in an alternative embodiment of the present invention and as shown in fig4 a timing circuit 44 may be included to interrupt the operation of the pump 12 if the pump has been running continuously for a predetermined period of time more specifically connected in series between the pump 12 and the operational level sensing switch 16 may be a single pole single throw electronic switch 46 which is controlled by a timing circuit 44 such as an ne555 timer for example the.