If accessible, you could tie into the headlight switch on the steering column instead of the headlight power - I don't know if robbing that circuit would be good or bad for just a buzzer. My habit is to avoid dedicated circuits like those.

The dome light is a good indicator with the door switch - you could also tie the relay into an ignition wire that's only live with the key turned. That way the logic would sound the buzzer if the lights are on and the car is off and the door is open - instead of just sounding the buzzer if the door is opened when the car is running.


Or a completely different option is to wire the headlights themselves to relays tied into the ignition wire. The logic would only send power to them if they are turned on and the key is turned to ACC or IGN.


oooo, I love relays and all their wires!

Good Luck.