I'm hoping there is a reasonably obvious answer to this. Here is my scenario. It's simple but I'm trying to over-explain it so that it's clear:
I've created a GPS tracker based on the Arduino Nano. I want to take action when someone opens the vehicle's door. This is an OLD vehicle that does not use a CAN bus. The wire in door jamb switch, connected to the interior lights, is always +12V, except when the door is opened, the door jamb switch connects to ground, completing the circuit. I will tap into this wire to sense a connection to ground when the door is open. I am using the vehicle's battery to power the Arduino.
So I would like to trigger an interrupt when I connect the interrupt pin to the vehicle's ground. Currently, I simply have the interrupt pin set as INPUT_PULLUP, and I have a diode allowing current from the Nano to the car, preventing current from the car to the Nano to avoid burning out the Arduino. I was considering also including a small resistor. I have a different solution involving a relay, but I'd like to avoid this.
Testing in my house, when I connect a 10 foot wire to the diode (nothing on the other end of the wire) the interrupt triggers just by tapping the wire to the diode. When I tap it with my finger, it also triggers. I was told months ago that it is likely the 110VAC mains of the house.
Basically, I want this interrupt trigger to be reliable and not wonky... falsely triggered by EMFs and whatnot. My background is in software, and I'm a novice hardware person compared to a lot of the people on this forum. Any advice would be appreciated.