Aftermarket keyless entry questions

I'm helping a friend out with installing an aftermarket keyless entry/ alarm system in his 93' PA (base model) I was wondering if anyone here knows whether the Buick uses a positive or negative door trigger? Also, I know that the interior lights are activated through the door lock actuators, but how does the "Door Ajar" light illuminate without a door jamb switch?....(assuming there is none, I couldn't find any!) I need this switch to wire either the positive or negative door trigger wire to set off the alarm in the event a door is opened while it's activated. I tried hooking both wires to the interior light circuit, however this didn't work because the alarm would still go off even after the car was running in park! Thanks for any tips and advise, this is our first time installing one of these!