Without looking... Guessing its the wash-in-use connection. Typical Car wash is active high or active low.. Meaning the Car wash changes the state of the output to high while washing a car. Drops the output when wash completed. The dropping edge is the signal to the Cashier to load the next wash. On top of that, some equipment will do a 1 second off-on-off then hold off with the signal during a wash fault instance. When the wash is cleared of fault status, then signal will go back to normal. Active low equipment is the same logic - just opposite as far as on vs. off. Older equipment just pulses the output when the wash is complete. That logic still works, but stacking isn't as smooth since the cashier never really knows when the car wash is washing the car - only when its done.