I’m in the process of putting an alarm in my 81 and can’t get the door pin switched to activate the alarm. I took this out of a 75 a few years ago so I do know it works. Would the interior light delay have anything to do with this?

 

Well just disconnect the wire that goes to the delay module temporarily. And see what happens.
On my 77 the factory alarm connects to the door switch, one of 3 wires and the module doesn't seem to affect the factory alarm in any way. So I kinda doubt it.

 

Thinking about it. Those 3 wires on my 77. I'm only guessing that a 81 would be the same . One wire is of course the alarm. Second wire is to the delay module. And the third wire is for the key buzzer circuit.
Any chance there could be an issue with the key buzzer circuit? You open the door with the key left in the ignition. Does the warning buzzer work?
Have you disconnected the wire that went to the factory alarm?

 

I made a temporary jumper bypass the light timer and got the door pin switched to work but based on the wiring setup I used I doesn’t make any sense how it’s working. I’ve been putting alarms in my cars for years,this alarm came out of a 75 I sold a few years ago. In the wiring diagram if I have both #6 and #8 together the pin switches work as they should. Positive and negative wires together does seem like it should work but it does. I’ve tried every way the hook up these wires and this is the only way they work.

 

Overall I'm not a fan of aftermarket alarm systems. I've removed far more than I have installed.
However, if you have it working, it's working. While the interior light delay is a nice feature. It's probably not all that necessary. On my 77 I upgraded the light delay from a capacitor that charged up, to a more modern board. I like the feature.
Bottom line is, happy to hear you have it working.