2002 Ford E 350 van

2002 Ford E350 van hi guys i have acouple of question i haven't done 1 of this yet so here it goes.... this van has a positive door trigger right. how would i connect a relay to an alarm that has a negative input for door triggers i know about the reverse polarity but how would i hook up the wires to the relay. sorry i'm kinda new to this :) and second i was thinking of connecting the door trigger by using 1 of the courtesy light for this. if i connect the courtesy light for the door trigger where and how would i connect the illuminated entry wire with a relay... to the same wire???? i have the door trigger connected too? this is all for a basic alarm system something like the viper 350

https://www.the12volt.com/relays/page1.asp