279 autowatch anti hijack connection

Can someone please explain to me how the connection works with the diode between the driver’s door and the passengers doors for the anti-hijack. There is only one wire (-) for doors,’ I don’t want the anti-hijack to kick in every time one of the passenger doors open. that’s where the diode connection comes in, but how will the passenger switches send ground to the alarm door wire if the diode is facing that direction shown on the diagram. according to my knowledge ground can only enter at cathode, so how will the passenger switches trigger the alarm if the diode gets connected like in the diagram. The positive side of the diode is facing the negative switch.    Mr signal

Diagram.     Http://www.google.com/search?q=279+autowatch+diagram&client=ms-rim&hl=en&channel=browser&prmd=ivns&source=lnms&sa=X&ei=Jtt1U42sFoSn0AWO2IHgCg&ved=0CAUQ_AUoAAMr signal