Tapping Dome Light Wires

[hayze]

I'm planning on tapping some 5mm LEDs into the ceiling of my TSX and would like to tap the dome light wires. Most people just find the dome light fuse in the fuse box, but my lights are going to be in the ceiling, and I'd rather not run the wires down the pillar. So I'd like to just tap the wires right in the ceiling wires (in the picture) instead. I need someone to look at this picture and see if they can help me figure a few things out.

Here is a picture of the back of the dome light frame after I took it apart:

1) I need to determine which wire is the ground (the red/green or the white/blue in the picture). I already know that the metal contact on the right (with the cover) is the positive. So if you look at where each wire goes and follow the metal paths, it seems as if the white/blue wire goes to the positive, and the green/red goes to the negative. Can someone tell me if I'm right. I'm probably going to have to get a voltmeter anyway, but I don't have one right now.

2) Another question: if these wires are before the switch (which is in the middle of the square case), then will tapping them there cause the light to always be on regardless of the dome lights? If so, then would I have to tap the wire onto the metal AFTER the switch to have the LED turn on/off with the dome light?

I'm wondering if anyone who is electronically inclined recognizes the picture enough to comment on my logic here.

Thanks for any help.

 

[jph]

I think one wire is hot all the time, and one is hot when the door is open (or it may only be a ground when the door is open).
Is there a metal contact where the screw goes on the other side of the assembly?

Just a guess.

 

[LukeA]

1. Testing it with a DMM is the only definitive way.

2. Yes. If you want to preserve stock operation then you want to tap the power at the stock locations. This is why my LED trunk light wouldn't turn off when I grounded it to the frame instead of the (-) on the connector.

 

[hayze]

I think one wire is hot all the time, and one is hot when the door is open (or it may only be a ground when the door is open).
Is there a metal contact where the screw goes on the other side of the assembly?

Just a guess.

Yes, there is a metal contact where the screw goes on the other side of the assembly, and it is connected to the contact that I suspect is negative. What does that mean?

2. Yes. If you want to preserve stock operation then you want to tap the power at the stock locations. This is why my LED trunk light wouldn't turn off when I grounded it to the frame instead of the (-) on the connector.

So I have to attach the LED wire to the metal AFTER the switch (between the light and switch) to preserve stock operation, right? Below, I pointed out which piece of metal I mean just for extra clarity:

Thanks for the replies

 

[jph]

1. Testing it with a DMM is the only definitive way.

+1

 

[LukeA]

So I have to attach the LED wire to the metal AFTER the switch (between the light and switch) to preserve stock operation, right?

Right. You'll get the same results as stock anywhere on the same piece of metal as the original contact (anywhere on the same circuit node, if you will), which is where you've pointed.

 

[Lynx_Arc]

I use a straight pin (like a sewing needle with a round plastic head) and stick that into wires and hook clip leads to a meter then turn things on/off open doors etc.

 

[hayze]

Actually, I'm just going to connect the wire terminals directly to the metal festoon contact clips (that hold the bulb in).

That way I would get completely stock operation.

Is this safe in terms of not causing a short or other damage?

 

[LukeA]

Actually, I'm just going to connect the wire terminals directly to the metal festoon contact clips (that hold the bulb in).

That way I would get completely stock operation.

Is this safe in terms of not causing a short or other damage?

Yep as long as what you put between the clips controls the current through it, i.e. it has a resistor or a driver. It's fused anyway.

 

[hayze]

So I'm assuming LED festoon bulbs with resistors will be okay in general?

What if the resistor in the LED bulb fails?

 

[LukeA]

So I'm assuming LED festoon bulbs with resistors will be okay in general?

What if the resistor in the LED bulb fails?

They'll be fine.

Resistor failure (under normal operating conditions) is not common at all and your typical metal foil resistor will fail open-circuit.

 

[hayze]

I asked about this on a TSX forum, and one guy just tied the LED wires to the festoon clips in the ceiling.

Is that safe to just tie them? Soldering would be difficult. Let me know what you think.

 

[Lynx_Arc]

if you are not drawing a lot of current (in excess of 5 amps) you can use those quick connects to tap in the circuit if done right they are just fine I think.

 

[Illum]

Wheres Darell when you need him
Admin Darell specializes in these things...

http://www.candlepowerforums.com/vb/showthread.php?t=17148

I'd give him a PM

 

[LukeA]

Wheres Darell when you need him

Who in this thread needs him?

 

[buickid]

I asked about this on a TSX forum, and one guy just tied the LED wires to the festoon clips in the ceiling.

Is that safe to just tie them? Soldering would be difficult. Let me know what you think.

Perhaps cut a piece of wooden dowel to length, and put two metal tacks in the end. The wires can be soldered to the underside of the tack.
Just an idea

 

[jhanko]

Just for the record, the white/blue wire is constant +12V. The green/red wire is grounded through the computer. The selector switch grounds the bulb through the computer with the green/red wire (door), or directly to the chassis via a screw (on).

 

[hayze]

You guys are an excellent source of information. Thank you.

Based on all your responses, I figured that I can tap the positive LED wire to the blue/white wire, and then attach the ground to the neg contact clip (after the switch). This will preserve stock operation.

Attaching the positive LED wire to the metal festoon clip makes it more likely that a piece of the wire will somehow touch the chassis and cause a short. So I should just tap into the blue/white wire and seal it up REAL good. This way, there will be no additional positively charged metal that is exposed that can touch the frame.

The frame is very close to the top of the dome unit (the first picture I took). This is why here is a cover over the positive clip.

Do you guys agree?

Thanks again.

 

[jhanko]

You guys are an excellent source of information. Thank you.

Based on all your responses, I figured that I can tap the positive LED wire to the blue/white wire, and then attach the ground to the neg contact clip (after the switch). This will preserve stock operation.

That will work perfectly. How you choose to execute it is up to you. You will be fine as long as you insulate any + slice points...

 

[hayze]

Awesome, this is starting to clear up very well for me.

So the positive needs sealed so it doesn't come unraveled and touch the frame. Got it.

What if the negative LED wire comes unraveled and connects the negative festoon contact with the frame? Since the negative is switched, then that would cause the light to turn on even though the switch is off, right?

thanks again