2004 gmc sierra door triggers

I'm installing an Autostart system 3 alarm in my 2004 GMC Sierra 2dr. and I'm stalled so far at the door triggers. I have found the door triggers for L and R which show 12V when the doors are closed and open circuit when the doors are open. I spliced into these wires and put a 1N4007 diode into each wire as per the isolating door triggers page. When I set it up as the negatve trigger the diodes block the voltage and there is no output. When I reverse the diodes as the positive diagram shows I get output on the individual wires (doors closed). When I join the diodes together as in the diagram I get no individual door response. If one door is closed the output on the line that would connect to the alarm is 12V which would not trigger the alarm until both doors are open. Clearly that is not right. How do I fix that?dn

Audiovox has the following information for that vehicle. All Door Trigger GRAY/BLACK (+) DRIVERS "A" PILAR

There two independent door triggers, L and R and that is the problem. I have to use both but send them to a common feed at the alarm. I also want to include the 3 doors in my contractors canopy which will have switches on the doors.dn

Use the all door trigger wire on the door input of the alarm. Use the instant ground trigger for the doors on the boxes.

I think I'll solve this problem by using magnetic reed switches for everything.dn

Wow.