Driver's Door Light

[NeoXon]

Hi,

I wanted to find out how that little lamp on the bottom of the driver side door is connected. I checked the cables that to go into the door on the white connector panel close to the footrest pad (this is a car with steering wheel is on left).

With opened door I checked the connectors one by one and checked which of those had +12V. Now I pushed the black little switch (it is pushed by the door when it is closed) and the +12V did not disappear on any of the wires (of course the other end of the multimeter was connected to a ground connector on the car).

However I found a connector on which I attached a small test lamp (12V, 3W) and it lights up when door is closed (switch is pushed), and goes off when door is open. This is exactly the opposite than what would be logical: +12V should be there when the door is open, that's why the little lamp ligths up in the door, am I right?

I could not figure out how this black switch works. Normally I would think a switch works in the following way: +12V comes in one a wire and a switched wire goes back that has +12V when the door is open, 0 V otherwise. But it has only one wire that goes in, and it has +12V. What does the black switch do then on column B when the door is closed? How can it "tell" the lamp that it should switch off? Is there some more sophisticated circuitry than a switch behind somewhere that detects if a very small resistor gets disconnected when the door is closed and when it is open, it can measure some resistance? I still wonder though how that lamp works then. I am quite sure it cannot light up when the voltage is 0 V.

update: does anyone know of a wiring diagram for Avensis 2004? It would be very cool to know where the wires coming out of the connector near the footrest pad are connected to.

[Jamesbelfast]

If the car has conventional lighting control there will be a permanent 12 volts to the door switch and then when the door is opened the voltage is switched to earth via the steel metalwok of the car body. It is known as earth switching. Quite a number of ancillaries work on this principle - wipers just being one example.:)

[NeoXon]

Does this mean that instead of switching +12V on and off (positive switching) I pull the GND up to +12V when the door is closed, so there's no voltage difference on the lamp and thus it does not light up, but when I open the door the car's GND drops back to 0 V so there's 12V difference on the lamp and it switches on?

Does this mean if the doors are closed, there's 12V on the metal parts of the car's body?

But that would make it possible to light up a bulb by connecting one and to the chassis (+12V when doors are closed) and the other end to car battery's -.

Or did I badly misunderstand something?

And how is that I can still light up a lamp no matter if the doors are closed or not if I connect a test bulb one end to the + of the car's Battery and the other to the chassis? If the doors are closed it should be at +12V so the test bulb would not light up.

How can I measure if it has ground or positive switching? Or I can know it only if I have circuit diagram?

[Pat2u]

I not been near a door light switch in years, but last time i worked on one the switch when pulled out of the door pillar had a single feed, and depending on neg or pos earth system of the vehicle was earth on the door pillar, bear in mind this was many years ago and on ford vehicles but i doubt the things have changed much these days.

[ministeve]

the easy way to test for a door switch wire on your car is to put one end of you test lamp on 12volts + and the other end test for door switch wire you are looking for a switched neg wire hope this helps

steve