Re: Wiring question

["Ron Buchalski" <rbuchals@xxxxxxxxxxx>]

Good suggestion.  If you have a wiring diagram for your car, it'll be much 
easier to find this.

Just be sure that the LED has a resistor in-line with it, to limit current 
flow through the LED, and keep the voltage drop across the LED within it's 
limits.  Connecting an LED across a 12v source will fry it.

Remember, I = E/R  or R = E/I

E = 12v
I = current through LED (should be less than maximum rated current)

So, you can determine the value of your resistor by solving for R.

- -rb

>
>Date: Thu, 14 Mar 2002 08:37:11 -0500
>From: "Michel Drainville" <MDrainville@domain.elided>
>Subject: Re: Wiring question
>
>On Tue, 12 Mar 2002, Paul & Diane Graveling wrote:
>
> > Can anyone help? I have an '88 E30 325i and I need a wire around
> > the dash area which I can use to supply an LED only when the key
> > is in the 'Off' position. (Not the 'accessory' position but
> > completely off, key removed). I've found a fused +12v line which
> > is permanently on, and now I need the switched negative side.
>
>
>You can use a relay like someone mentionned before but it's not required.
>
>Find a relay or bulb that receives 12v when the key is in ACC AND IGN. If
>it's a relay, find the two terminals for the coil. One of them will be
>connected to ground, the other will receive 12v only when the ACC is turned
>on.
>On the LED, connect the positive to a fused 12 source (constant 12v) , and
>the other side to the switched 12v of the relay (or light bulb).
>
>When the ACC will be ON, the LED will see 12v on both side so it won't
>light (no voltage drop, no current), when the ACC will be OFF, one side of
>the LED will be to 12 volts and the other side to ground (via the coil or
>bulb) since the resistance of the relay coil or bulb is very low compared
>to the LED resistance so it will act like a simple wire. And just in case
>you wonder, no the relay or bulb won't turn on because there will be
>something like only 0.3v on it.
>
>Hope this helps.
>
>Michel Drainville
>91 318ic


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