It doesn't ... Refer earlier test that I did and amended Image.

Confusion for anybody reading this is calling Ajar, Jamb and Jamb, Ajar.
As per the AIM, there is a Hood Switch, a Jamb Switch/Courtesy (located at the footwell) and Ajar Switch (located as you enter the vehicle, the one you get your clothes caught on)

 

If you PM me i'll send you a copy of the '73 Wiring Diagram which should answer all your Prayers.
Your wiring can not be exactly when you have an addition. Your Door Jamb Switch (drivers side), contains a White Wire for courtesy lights and a Black Wire for earthing your Key Buzzer Switch in your steering column and the passenger Jamb Switch has one White Wire for coutesy lights (these White Wires ground on the body of the vehicle, NOT the Black Wire).
Your Ajar Switches on the other hand have three wires, Black, Lt Blue and White (Black is various Earths, Lt Blue Alarm and White courtesy lights). I have two wires at my Hood Switch, a Black and a White.The door Jamb Switch you refer to is the Ajar Switch which in my previous photo was used to show that I have Lt Blue and White and NOT Black and White as per your Wiring Schematics. My Ajar Switch has in fact got Black, Lt Blue and White on both sides of the vehicle.

 

You have several errors in that post about what you think I said, but I am only going to point out that I didn't add anything to my wiring, I only added the blue COLOR to the diagram to denote the ajar wiring. The black wire at the switch runs to the frame ground and grounds both the white wire for the alarm and the blue wire for the door ajar light. You can't ground to a car body when that body is fiberglass. The door ajar light only lights when the key is in run, and the alarm only has power when the switch in the rear is set. The lt blue wire is for the door ajar light, the white wire is to trip the alarm by grounding it to the black wire, which as I said is going to the frame. The colors on the diagram are correct, check out the white wires going to all three alarm switches. The courtesy lights work off the other switch at the front of the door opening, and that's the only thing it does.
I think we've covered everything necessary for anyone to troubleshoot their alarm, we have provided the diagram, the description and the proper operation of the alarm circuit. That was the purpose of adding info to the old post in the first place. I will post no further here, if anyone is looking for help with the alarm circuit, pm me and I would be happy to help.