Note: It's advisable to use a diode in both configurations or you could get a continuous current drain through the courtesy light, buzzer and parking lights, when the lights are off and the doors closed. Polarity of buzzer (if polarity sensitive) and diodes are shown for negative ground cars, for positive they should be reversed.

Inset 1: This avoids cutting factory wiring but causes both passenger and drivers doors and the courtesy light manual switch to sound the 'lights on' warning. NB. Miles Bannister has pointed out that the original schematic for Inset 1 didn't include the diode and this would result in the drain referred to above. My (weak) defence is that I have never used Inset 1, I only included it for those people that didn't want to cut a factory wire. The diode solves the problem, thanks Miles. If the diode is accidentally reversed the buzzer won't work, but you will get the drain referred to. Updated September 2010: Note that polarity sensitive buzzers may block this reverse current drain, you would have to test your buzzer with an ammeter. Measure the current in the normal direction i.e. buzzer sounding, then measure again with the buzzer connections reversed (which shouldn't harm the buzzer). If there is no current flow when connected in the reverse direction then you don't need the diode in this configuration.

Inset 2: This arrangement results in only the drivers door sounding the buzzer. The diode prevents current flowing through the buzzer to the ground from the passenger door switch, and it is this that causes the buzzer to ignore the passenger door. It must be inserted between the drivers door switch and the branch to the courtesy light. To avoid cutting into wiring you can make up a diode with two bullets and an additional 2-way connector and insert it where the wire from the drivers door switch joins the wires from the passenger door switch and harness at the 4-way connector behind the centre console. NB. Darren Lewis has just (September 2004) advised me that originally (and for the past four years!) the diode was shown connected the wrong way round for the negative ground car shown. It is now correct. Thanks Darren. If the diode is accidentally reversed the courtesy light will only respond to the passenger door (and the manual switch), not the drivers door. Note this diode is required irrespective of whether your buzzer blocks the reverse drain current.

Diodes showing how the markings relate to the schematic symbol, i.e. the marked end (red blob, thick silver band) denotes the pointed end of the 'arrow' symbol, and the direction of the arrow indicates the direction of conventional current flow i.e. from +ve to -ve. Note the one on the left is a Lucas (yes, that Lucas) diode, the other is the type you are more likely to find these days: