The Germans obviously don’t suffer from the absent-mindedness that afflicts me
more and more as the years go by. Neither my BMW nor my Carrera 4 have any
warning system to tell you that you have left your lights on, and the lights
don’t go off with the ignition. As I drive with my lights on quite lot, I was
heading for a flat battery.
So I have fitted a warning buzzer that sounds when the drivers door open and the
lights are on. It has only three components and will cost about £3 including all
the wire etc.
You can get all the parts you will need from
Maplin - the codes in brackets are Maplin
order codes, though you’ll pay more in P&P than you will for the bits!
 | 12v Buzzer (FL40T) |
| Low current diode (almost any will do) 1N4001 (QL73Q). I actually used MR571 for both diodes as I had them in stock... it makes the job about 10p more expensive! |
| High current diode MR751 (YH96E) |
| A few bits of wire, a couple of screw top connector blocks, and one of those clip together “cable lock connectors” usually in blue plastic and available from Halfords. |
| As the door switches get unreliable with age, I suggest you get a new set of door switches (£17.52 incl vat and delivery) from Bert Gear at Berlyn - I didn’t at first and had to drive a few miles with the buzzer sounding - not a pleasant trip! |
Study the diagram for wiring below and away you go.
The buzzer is polarised so you should connect the low current diode stripe end to the red wire and wire the other end of the low current diode to the light switch. It’s easiest to remove the light switch by pulling off the knob, and then unscrewing the bezel using a pin spanner, or some point nosed pliers, the switch will drop out of the back of the dash.
On my car the wire you want to connect to is grey with a black stripe, but this may vary, so it may be best to test the wire with a meter - it should be live when the lights are on, and not when off. Tap into the wire using the cable lock connector and run a piece of wire to the low current diode, connect using a screw top connector block. the black wire from the buzzer then connects to the cable from the drivers door switch.
f you test at this point you will find that the buzzer will sound when either door is opened, which is irritating when you let passengers in and out, so you then need to fit the high current diode in series with the door switch with the stripe end towards the switch (see diagram).
The drivers door switch wiring can be found by removing the carpet panel behind the front boot release handle. You are looking for a brown wire with a white stripe down it. You may find alarm wires spliced into this wire (I did) and you should make sure your mods are between this point and the door switch.
When I fitted the new switches I replaced the wire from door switch as the original was somewhat chafed from previous work, this makes life easier as you can fit a longer piece and this gives more room to work.
Finally tuck away all your new wiring, and find somewhere to lodge the buzzer. Put the carpet panel back, and its done!
