If headlight power it taken from dash lights instead, you could control the volume or turn off the alarm, when you want to have headlights on with ignition off, by dimming or turning off dash lights. 87a is a normally closed contact with 30. Relay is a very common automotive relay available at auto stores or Radio Shack. Also called a Bosch relay. There are several of these relays in our coach and generator.
Most modern vehicles have inbuilt headlight alarms or automatic headlight switch off functions. Older vehicles do not have these features and can have a flat battery if the headlights are left on when the vehicle is turned off. There are many headlight alarm systems available ranging from simple to complex & expensive. Shown below is a very simple method to sound a buzzer if the ignition is turned off while the headlights are turned on.
All that is required is an automotive change-over relay and a buzzer. The diagram shows the relay pins as viewed from the pin end of the relay. (If preferred, the headlight power connection could be connected to park light power instead, which will alarm if headlights or park lights are left on). www.redarc.com
I went to the local auto parts store and bought a buzzer made just for that purpose. It was probably just a 12-volt buzzer with a diode in series with the leads. I wired it between the headlight lead and the ignition lead, and when the headlights were on at the same time the ignition was off, it got 12 volts and reminded me to turn them off. Tom Lang 2003 U295 M3810