diodes in starter kills

Is it really necessary to use a diode when installing a starter kill? What is the diode actually protecting in this situation? Exactly how do you wire the diode into the circuit, or do you have to have a relay with a diode installed?

Its called a spike supression diode. It is there to prevent the voltage spike that occurs when the relay get triggered. I have seen some installers install a starter kill without one, but I wouldn't do it. they make relay harnesses with them built in, or you can do it yourself. heres how the relay works for a starter kill. pin 87 gets left empty pin 87a get the switch side of the starter wire, pin 30 gets the car side. pin 85 gets the ignition input pin 86 gets the ground when armed from your alarm. put the diode between pins 85 and 86 with the strip side facing the ignition Northstart.....or start it your damn self.