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Wiring LED footwell lighting to multiple power sources

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Rownan

Joined: Aug 06 2013
Posts: 5


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Post Tue Aug 06, 2013 1:28 pm

Hey all, I put in some LED footwell lighting in my Focus about a year ago, all bought from Oznium. I wired it up with help from this forum, so first of all thanks for that!

I've been happy with it, but at the moment it is only powered by the airbag circuit (which is powered whenever the ignition is on). I now want to make the LEDs come on when I unlock the car and open the doors. To do this, I decided I would tap into the parking lamps.

At the moment, all I have is a simple fuse tap on the airbag circuit wired to a dimmer control knob, which outputs to the LEDs.

Looking at most of the posts on here, it seems that using a relay is the suggested method, but these LEDs pull such low current... Do I really need a dedicated 12v line for this? Seems like I can wire in a feed from the parking lamps to the existing terminal on the dimmer control and use diodes to prevent bridging the circuits.

See attached diagram. Sorry I am a noob when it comes to electrical so I hope this is clear enough.

User posted image

Will this work? My only thought is.. What about when BOTH circuits are powered (which will happen anytime the parking lamps are on AND the ignition is on). What happens?

Thanks a LOT for any suggestions!
Aken

Joined: Feb 12 2003
Posts: 10885


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Post Tue Aug 06, 2013 9:27 pm

Whether or not you need a relay depends on your power sources.

In theory, your diagram would be fine, if that's how your car is wired up. Some lights and electronics in a vehicle are negative switched, not positive switched, so determining that will show you your options for wiring the parking lights into your existing source.

As for if both power sources are on at the same time -- if they're the same source type and voltage (a la 12v DC), then that's fine.

Figure out where you are going to retrieve the parking light signal, verify what voltage and such you're working with, and that'll determine if your wiring diagram will be sufficient.
Rownan

Joined: Aug 06 2013
Posts: 5


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Post Wed Aug 07, 2013 10:13 am

Alright, thank you for the insight.

I know I ran into the posivitely switched vs negatively switched issue the first time around, it took me a bit of trouble to find a circuit that was both positively switched and hot at the times that I wanted the LEDs to light.

From what I gather, the parking lights are computer controlled, so the option for tapping the parking light signal is going to be up near the headlight I think.. I am assuming at this point that it is positively switched as well (I am actually not 100% certain).

Then I just need to figure out a way to get the wire through the firewall and into the dash where my dimmer control is.
bad venge

Joined: Jul 28 2007
Posts: 3550


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Post Wed Aug 07, 2013 12:50 pm

I'd tap power from the supply of the dash lights before the dimmer
Rownan

Joined: Aug 06 2013
Posts: 5


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Post Thu Aug 08, 2013 7:11 am

bad venge wrote:
I'd tap power from the supply of the dash lights before the dimmer


That's an interesting thought, I'll have to find out where the source is on that. At least then I'd be able to keep everything within the cabin.
bad venge

Joined: Jul 28 2007
Posts: 3550


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Post Thu Aug 08, 2013 5:12 pm

Find the dimmer , check with voltmeter find the 12 volt leg and use it
Rownan

Joined: Aug 06 2013
Posts: 5


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Post Thu Aug 08, 2013 6:47 pm

bad venge wrote:
Find the dimmer , check with voltmeter find the 12 volt leg and use it


Looks like the factory dimmer module is not a switch per-se, but a digital controller for the BCM computer. I'm not sure what the wiring looks like, and if there's a 12v leg to tap.. I am trying to figure out how to get to the back of it.

Something I DID learn though, that BCM apparently has a feed to the parking lamps, and the BCM is behind the glove box somewhere.. So I could potentially tap the parking lamps from within the cabin.

However, I think I like the idea of tapping the dash lights even more.. having them on the same circuit will look more factory stock.
Rownan

Joined: Aug 06 2013
Posts: 5


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Post Sun Aug 11, 2013 6:16 pm

Confirmed, the dimmer switch has three wires coming out of it (the same console also controls headlights, fogs, and hatch release).

One is green/purple and is sending data to the BCM. Then there's a ground, and a power. I put a voltmeter on the power and it's constant on.

I'll wire into the parking lamp feed like I planned earlier.

Thanks for the help!
Tat2Dragons

Joined: Jan 21 2007
Posts: 3404
Location: Baltimore Maryland


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Post Tue Aug 13, 2013 12:33 pm

Rownan wrote:
bad venge wrote:
I'd tap power from the supply of the dash lights before the dimmer


That's an interesting thought, I'll have to find out where the source is on that. At least then I'd be able to keep everything within the cabin.


I would think the easiest way to go about that would be to tap into the 12volt source for the HVAC lighting.
bad venge

Joined: Jul 28 2007
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Post Tue Aug 13, 2013 12:39 pm

most of that's on a dimmer , then you either burn the dimmer out or not have full voltage for dimmed leds
Tat2Dragons

Joined: Jan 21 2007
Posts: 3404
Location: Baltimore Maryland


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Post Tue Aug 13, 2013 12:42 pm

bad venge wrote:
most of that's on a dimmer , then you either burn the dimmer out or not have full voltage for dimmed leds


My bad, I guess I should have payed more attention to the question. icon_smile.gif
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