occurrence to be outputted by the display 16 also shown in particular is the charging circuit 60 connected by the stop jack pair 22 to but not at all times electrically influence the wet contact touchpad 11 the charging circuit 60 which also functions as a charging current switch includes power transistors 62 and 64 and resistors 66 68 and 70 a 70 n the output of the charging circuit 60 is controlled by the microcontroller 18 to either provide or not provide charging current to the wet contact touchpad 11 as explained later in detail in the stop circuit a diode 72 provides a low impedance path for the charging current from the charging circuit 60 out to the wet contact touchpad 11 while blocking any signal that a user may inadvertently connect to the input at the stop jack 22 resistor 74 allows the voltage on each side of the diode 72 to equalize while still maintaining a high impedance to any signal the user may connect a zener diode clamp 73 prevents the voltage from exceeding a predetermined value which could damage the inputs of the microcontroller 18 transient voltage surge suppressors 75 a 75 n are incorporated as protective devices across the leads from the circuitry connecting the start jack 20 the stop jack 22 the reset jack 24 and the horn jack 26 to quickly react to voltage spikes by shunting any spikes to ground to avoid damaging the inputs of the microcontroller 18 the overall circuit can function satisfactorily without the transient voltage surge suppressors 75 a 75 n.