Negative input trigger = the alarm will go off when this wire is grounded (hits the negative terminal on the battery, touches a metal part of the vehicle, etc)
Positive Input Trigger = the alarm will go off when this wire hits a positive input--the big red wire coming from your battery.
You just have to figure out if the wire you are splicing into is negative or positive when it needs to be.
okay, example--you want door triggers. find the wires that go to your dome light. when the door is opened, the dome light gets power, so you would want a positive input trigger there.