Wiring Footwell LEDs: Using Diode, Switch, and Ground on Negative-Switched Circuit

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#31 21663876 27 Sep 2012 14:45

Steve Lawson Steve Lawson

Anonymous

Post #31
21663876 27 Sep 2012 14:45

bq). So when the car is off, would the ground function still? Or no?

When you say "the ground" I'm not sure what ground you are referring to, BUT, the ultimate answer to your question is, experiment! Because, even if I did know what ground you are referring to, I would probably still say "experiment!", because I don't know how your car is wired.

bq). What I mean is, when the door is closed, and the gray wire functions how it does, if that indirectly is attached to the cigarette ground, would it mess up the cigarette lighter where I would need a diode? Similar to the reasoning behind needing one for the domelight.

That all depends on whether or not the cigarette lighter ground is ever interrupted by anything. I doubt if it is, but you have brought that into question, so I suggest you test it and find out. If it's a solid ground (i.e. an uninterrupted connection to the negative side of the battery) then no worries. Nothing is going to change that (short of some MASSIVE current, and unless your LED lights can be seen from outer space, I doubt that is an issue ;)

bq). As for the relay, the intention was for it to be grounded when the door opened. So it actually functions fine. Its just because of the dimming it clatters. The way the relay is currently set up actually is a lot more intensive then I have described, but it is irrelavent.

You said yourself that it isn't _fine_ because of the chattering. I think you're making it more complicated than it needs to be. But, if it's irrelevant, then I won't go there.

bq). Knowing my absolutely idiotic mistake, how does it sound?

Assuming the cigarette lighter ground is a solid ground, then just use my circuit diagram (reproduced below). Besides, how am I suppose to comment on "how it sounds" when I don't know the nature of your "intensive relay setup"? And, in fact I don't want to know about your setup. If the truth table is correct, then just use my diagram.

bq). Actually I see one with 400 PIV for $.30 more. So that ought to work. As long as PIV=PRV

Yes PIV=PRV. And, yes, that sounds like the correct diode. And I would pay the extra $.30
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#32 21663877 27 Sep 2012 15:29

Billy Roberts Billy Roberts

Anonymous

Post #32
21663877 27 Sep 2012 15:29

The reason the relay is irrelavent is because while it functions, its not how I want it so I am dissassembling it later.

_That all depends on whether or not the cigarette lighter ground is ever interrupted by anything. I doubt if it is, but you have brought that into question, so I suggest you test it and find out. If it’s a solid ground (i.e. an uninterrupted connection to the negative side of the battery) then no worries. Nothing is going to change that (short of some MASSIVE current, and unless your LED lights can be seen from outer space, I doubt that is an issue _

With this question, I shall explain a bit better.

The gray wire, when opens, is grounded. When shut, it does what it does, which I'm not clear on.

This gray wire will be the basis for the circuit to the LEDs as the negative wire. The switch will connect the ground from the cigarette lighter to the circuit coming off of the gray wire. So, when I flip the switch and ground the circuit, gray wire would also be grounded. So, I'm wondering, conversely, would whatever the door is doing when its closed go through the switch to the cigarette ground?

It may not actually effect it, but should I still prevent this from happening? Or will it?

The diodes came in a two pack, is there any reason not to install one there?
#33 21663878 28 Sep 2012 01:17

Steve Lawson Steve Lawson

Anonymous

Post #33
21663878 28 Sep 2012 01:17

bq). When shut, it does what it does, which I’m not clear on.

Each door has a switch that grounds the gray wire whenever that door opens. That's why the dome light comes on. When all the doors are closed, all of the door switches are open, which is why the dome light is off, and why you measure 12V on the gray wire when the doors are closed. When one of the doors is open, you measure 0V on the gray wire, because that door's switch has grounded the gray wire.

bq). The switch will connect the ground from the cigarette lighter to the circuit coming off of the gray wire.

Wrong, The switch will connect to the negative side of the LED arrays, BUT, the negative side of the LED arrays will ALSO be connected to the gray wire via a diode. That will cause the LEDs to light whenever one of the car doors opens, even if the switch is open. [assuming your truth table is truly true]

bq). So, when I flip the switch and ground the circuit, gray wire would also be grounded. So, I’m wondering, conversely, would whatever the door is doing when its closed go through the switch to the cigarette ground?

No. The cigarette ground is already at ground (assuming it's a solid ground), so grounding it will not change anything. But, that is mute, because the diode will actually prevent that path.

bq). It may not actually effect it, but should I still prevent this from happening? Or will it?

It won't affect it if you use the diode as I indicated in my diagram (copied below). And, actually, my diagram is the same as yours, except for the addition of the relay.

bq). The diodes came in a two pack, is there any reason not to install one there?

You only need one diode.

Caveat: All of this is true only if what you have been telling me is true. I'm basing all of this on the information supplied by you.
#34 21663879 28 Sep 2012 06:21

Sarah Harris Sarah Harris

Anonymous

Post #34
21663879 28 Sep 2012 06:21

the ground for your cigarette lighter will be a solid uninterrupted ground, earth whatever you want to call it. my main concern which i pointed out earlier is the fact that you have an auto dimmer. these are sometimes controlled by the main ECU (the expensive bit under the bonnet ) which i would be very cautious about applying an external voltage source to. hence my schematic attatched. although the grey wire becomes earthed when the doors open, the dome light wont be putting its current through it to illuminate, the grey wire will only be triggering the delay module and also any alarm system fitted.
any supply for the foot well lights should be taken from a "safe" known supply, ie the dome light.
I'll shut up now
steve, your patience is commendable
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#35 21663880 28 Sep 2012 06:29

Sarah Harris Sarah Harris

Anonymous

Post #35
21663880 28 Sep 2012 06:29

pic wouldnt load ??
#36 21663881 28 Sep 2012 08:10

Billy Roberts Billy Roberts

Anonymous

Post #36
21663881 28 Sep 2012 08:10

To be clear, the relay is meant to make the cigarette lighter ground only come to the switch when the car is on, right? and then its got the ground from the cigarette lighter as input and outputs to the switch.

Is that right?

Hopefully Ill be installing all this today. I truly appreciate the help.

Also, doesn't the diode take care of what Sarah is talking about? or no?

I don't want to mess that up obviously.

Also, Mrs. Sarah, the dome light currently is powered by the gray wire. You seem to be saying not to?
#37 21663882 28 Sep 2012 13:47

Steve Lawson Steve Lawson

Anonymous

Post #37
21663882 28 Sep 2012 13:47

Sarah has a point -- I didn't think of that. It is definitely not a good idea to use the pink wire to power the LEDs. If the ECU can't handle the extra load imposed by the LEDs I'm not sure what the result would be, but if it burns out, then, like Sarah said, it could be an expensive repair.

Thus, instead of the pink wire (as convenient as it is) you should connect directly to the positive side of the battery. But, as far as I can tell, Sarah's diagram also has the LEDs drawing current from the car's computer (via the pink wire).

I have revised my diagram, see below. There are two versions. The simpler one, and the safer one. The safer one is the one with the two relays. I indicate a 1N4004 but you can also use the 3Amp one if you already bought it.

The reason for the "safer one" is, I can't be sure how much current the door switches can handle. Sorry I didn't think of this before. Sarah set me strait
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#38 21663883 28 Sep 2012 13:51

Billy Roberts Billy Roberts

Anonymous

Post #38
21663883 28 Sep 2012 13:51

If you look here: http://www.toyotanation.com/forum/326-10th-ge...-illuminated-footwells-cupholders-switch.html

Its pretty much what I have said I want, I was just clarifying that its ok to connect the cigarette lighter and gray wires through the led wiring.

So if they are able to power them, I should be alright with this as well, shouldn't I?

I definitely don't want to mess anything up of course.

But, even if it couldn't handle it, shouldn't the fuse simply blow?

EDIT: Looking at your diagrams, when I had the gray wire and a positive from the cigarette lighter connected to the part of the relay that activates the coil, thats what clicks. So it won't be able to be set up like that.
#39 21663884 28 Sep 2012 14:18

Steve Lawson Steve Lawson

Anonymous

Post #39
21663884 28 Sep 2012 14:18

Holy mother of total dismay... it might have been nice to have seen that link long before!!

Looks like you've got everything you need.

BTW: there might not be a fuse -- and if not -- fried computer -- very expensive.
#40 21663885 28 Sep 2012 14:26

Billy Roberts Billy Roberts

Anonymous

Post #40
21663885 28 Sep 2012 14:26

Well the guy at our audio shop seemed to think a diode wouldn't work and I needed a relay.

So if they were able to use the pink wire for their LED strips and they seem to be fine, I ought to be ok to use it, right?

And if I am going to have problems it would be immediately apparent, right?

Finally, if there is a fuse am I definitly good to go?

I am looking in my owner's manual and there is a 10 A fuse called DOME which powers trunk light, smart key system, interior light. I know if the pink wire is cut that the keys don't work so that must be these. So do you think I am safe to go?

I TRULY appreciate the assistance and realize I have been a bit of a pain. For that I apologize, I am just being super thorough.
#41 21663886 28 Sep 2012 20:13

Billy Roberts Billy Roberts

Anonymous

Post #41
21663886 28 Sep 2012 20:13

Got it done! Works like I planned! So cool! Thanks to you both!
#42 21663887 29 Sep 2012 02:09

Steve Lawson Steve Lawson

Anonymous

Post #42
21663887 29 Sep 2012 02:09

Awesome!

Did you connect the LEDs to the pink wire?
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#43 21663888 29 Sep 2012 05:54

Billy Roberts Billy Roberts

Anonymous

Post #43
21663888 29 Sep 2012 05:54

I did. Since everyone else did and ti works, and there is a fuse I decided to.
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Topic summary

The discussion centers on wiring footwell LED strips in a vehicle using a negative-switched circuit involving a pink positive wire and a gray negative wire that is grounded when the door opens. The main concern is whether a diode is necessary to prevent backfeeding current that could activate the dome light or damage the cigarette lighter circuit. It is clarified that the pink wire is always 12V positive, while the gray wire is normally at 12V but is grounded when a door opens, completing the circuit and turning on the dome light. The LED strips are commercial 12V types with built-in current limiting, so no additional resistors are needed. The diode is recommended if the footwell lights are to be controlled both by the door opening (grounding the gray wire) and independently via a switch that grounds the gray wire through the cigarette lighter ground. The diode prevents current from flowing back into the dome light circuit. However, if the footwell lights are wired in parallel but independently grounded, a diode may not be necessary. The cigarette lighter ground is generally a solid, uninterrupted chassis ground, but its availability when the car is off depends on the vehicle wiring and should be tested with a continuity tester. Using the pink wire to power LEDs is convenient but may risk overloading the vehicle's ECU or fuse; a direct battery connection with appropriate fusing is safer. A relay can be used to control the ground supply to the switch, activating only when the car is in ACC or ON position, preventing unwanted LED operation when the car is off. The relay coil should be connected to a switched power source, not the gray wire, to avoid relay chatter caused by dimmer circuits. The discussion includes truth tables to define desired LED behavior based on door and switch states. Overall, the consensus is that with proper diode placement, relay use, and testing of ground availability, the footwell LED installation can be safely achieved without damaging existing circuits or causing shorts or fire hazards. The user successfully completed the installation using the pink wire and a fuse-protected circuit.
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