resistor based door triggers

You still need to sense voltage tho... (?) Re above, KP thought the resistive voltage divider might load the original circuit and also offered an alternative method. I explained why there is no loading and why resistor tolerance doesn't matter else is compensated. I didn't compare what loading a zener would add (I suspect more than uA), but I think I gave a good argument for using the cheaper and common "universal" input circuitry - ie, 2 resistors, 2 voltage protection diodes and an optional filter (cap). But KP's zener suggestion is a clever solution that is often overlooked - eg, for dropping voltages aka expanded scale applications, or when using discrete components.

I do need to sense the voltage, but only if the BCM is awake. When a door opens or the factory remote sends a command, the BCM wakes up. This would turn the circuit back on. I would just need to find a +12V source that the BCM shuts off when it goes night-night. Ahh, gotcha! I never truly understood the Zener diodes. I had to use one for the ignition module because one of the relays needed a 1 second delay before being energized. I was lost with that part of the circuit, but followed the schematic to the exact specs.No question is stupid or not worth asking. You were once a noob, right? :)

Alright, so I finally got a handle on how this car works. The BCM will turn off in 10 minutes if the car is armed with the factory remote. The BCM will sleep in 30 minutes if the car is not armed with the factory remote, but locked with the power lock button. This does not arm the factory alarm. Now for the fun part! There isn't a single circuit that is +12V and controlled by the BCM. The couple I found that are, are extremely low current and connecting anything to it will bog down the circuit and the BCM will 'protect' itself by shutting down the circuit. There's an exception: the dome light circuit. So the dome light works as follows: The BCM controls the +12V via a relay. This relay is located on the back of the fuse box at the driver's door. There is a RED / grey wire coming from the BCM that handles supplies the +12V output for the dome lights. The light bulbs are controlled by ground through the switches. The BCM keeps the +12V output alive until it goes to sleep. Here's the caveat: When the BCM sleeps, the voltage floats between .5V and 3V. This will screw with the circuit we built. The fix is to use a relay. Pin 86 goes to the RED / grey wire, and pin 85 goes to the alarm's GWA output. Now, the relay is only turned on when the system is armed AND the BCM is awake. As soon as the BCM sleeps, the relay shuts off, hence shutting off the LM339 circuit. I haven't decided yet whether pin 87 is going to be (+) or (-) to control the circuit. This is going to have to be trial and error to see which one confuses the LM339's, which is the problem I had before (when you remove power, the LM339's get confused and float(?) even though voltage is being 'pulled' to the outputs). I'll report back later with a full pinout, description of where everything goes, how it works, and whether this is fully successful or not.No question is stupid or not worth asking. You were once a noob, right? :)