Re: Wiring question

["Michel Drainville" <MDrainville@xxxxxxxxxxx>]

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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