I have noticed that when I unlock my car the interior lights come on, however, when a door is opened the lights dim slightly. Can anybody explain why this is? Surely you would like it to get brighter not darker?

 

The cause of this is common to many cars. The reason is resistance. When you unlock the doors, a relay under the dash turns the light on. The wires from the light to the relay are fairly short. When you open the door the door switch becomes the circuit path for the light. The wires going to the door switch are longer since they are strung out into the door. Since the wires are longer, there is more resistance and more power is used up in the wiring itself, taking power away from the light bulb. Therefore the light gets dimmer when you open the door.

 

[QUOTE]Originally posted by S2Kman
[B]
The cause of this is common to many cars.

 

Pinky:

You are right, If a person didn't know electronics that could sound like a pretty rediculous explanation. If they would put bigger wiring in to the door switch, or use the switch to operate the same relay as the alarm circuit then they wouldn't have the dimming problem. Some of the newer cars are using transistors on dome lights, and they do this little fade-out trick with it when you close the door. I had a '00 civic rental while my S2K got the grind fix, and it has a transistorized slow-fade on the dome light.

 

God! I wish I was this clever!

 

Anyone care to calculate the amp drop for that extra few feet of wire in the circuit? For say 10 gauge?
Nice to see there are a few sparkies here........

 

You have just entered the Twilight Zone!

 

[QUOTE]Originally posted by S2Kman
[B]
...The wires going to the door switch are longer since they are strung out into the door.

 

Of course it would depend on the amperage you're trying to pull and the temperature would matter too (a resistance would be a better way to describe the losses but wouldn't necessarily be constant due to load and/or temp). In this case not enough to make a difference, I don't think (less than 1 amp draw).

The dimming could be due to the diode deal, but might also be due to the extra resistance through the pin switch at the door as the alarm circuit latching function releases. Those pin switches can eat up the equivalent resistance of a spool of wire or more even when they are new.
Wait till they get crudded up!!!!!!!!!!!!!!
I'm sure some have experienced the old Chevy door switches that can double as a dimmer switch, but not on purpose.


[Edited by RT on 02-05-2001 at 12:02 AM]

 

Now isn't it because you don't need as much light when you open the door because you're letting in light. Very clever, these Japanese!