DIY Car Light Reminder

Some older cars donít have a buzzer to remind you when you have left your lights on. This cheap and easy to build kit will remind you if you have left your lights on as soon as you switch off the ignition.




Maplin code

Approx cost


12V Buzzer

FL40T or FK82D



12V SPDT Relay

UG42V or YX94C



Telephone cable or anything you have lying around




Epoxy resin



How it Works

The idea is very simple. When the ignition is on the relay holds two contacts apart. When the ignition is switched off the contacts close and connect the buzzer to the light circuit. If the lights are on then the buzzer sounds.


The picture below shows where to solder the wires.

When soldered use the epoxy resin, Araldite, silicone sealant or whatever you have lying around to cover the relay contacts so that they cannot short against anything when fitted.


A good place to fit this kit is behind the stereo if there is sufficient room because there is convenient wiring which can be tapped into.

Most radio installations only come on when the ignition is on. There will be two positive supplies. One will be continuously on to enable the stereo to remember its setting while the other will come from the ignition switch. It is this latter positive connection that you need touse.

There is normally also a wire from the lights which goes to the stereo which is used to dim the stereo display at night.

The relay and buzzer are small and quite light. In the past I have stuck then behind the dashboard area using double sided sticky foam pads.