LED Headlight, Turn Signal & Brake Wiring

OptimizePrime

Goblin Guru
Full disclosure: this is not my realm of expertise, I'm effectively handicapped when it comes to understanding some of this stuff but I could use your help!

I'm not using the standard headlights, sideview mirrors, or rear lights and this creates a 'fun' opportunity for me. While searching, information is spread between threads waiting to be found like the needle in a haystack. For those who are planning to go down this route, my goal is to consolidate the headlight, sideview mirror, and rear brake light wiring here. For those of you who have done it, any advice is much appreciated.

I have a 2010 Cobalt SS TC

HEADLIGHTS

FunctionHarness Wire Color
High BeamWhite
Low BeamYellow
Park LightBrown
GroundBlack

I have your basic two wire (ground - black, power - red) headlights. I have them wired as follows: Black = Black, Yellow = Red. I do not have a high beam or parking lights.

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TURN SIGNALS / SIDEVIEW MIRRORS

FunctionHarness Wire Color
GroundOrange
Turn SignalGreen
Park LightRed

I have your basic two wire (ground - black, power - red) turn signals. I have them wired as follows: Orange = Black, Green = Red. I do not have parking lights on my turns.

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REAR LIGHTS
DRIVER SIDE / PASSENGER

FunctionHarness Wire Color
Turn Signal & BrakeYellow / Dark Green
Park LightBrown
ReverseLight Green
GroundBlack

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I have four wires coming from my tails -- since the cobalt used the Yellow wire for Turn Signal & Brake how do I wire the Red & Yellow LED light wires to it? How do I go about figuring out the size resistor? halp

Answer: 100ohm resistor on the Park Light (White) which is then wired to the headlights - when you turn your headlights on the brakes will light up a dim red and not bright red like when the brakes are engaged. LED Red wire goes to the default Brake wire (Yellow / Dark Green). LED Yellow goes to the sideview mirror turn signal.


LED FunctionLED Wire Color
GroundBlack
Park LightWhite
BrakeRed
Turn SignalYellow
 
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Ross

Goblin Guru
I didn't add a resisitor to the rear LED tail lights, just hooked them up to 12V.
So take your rear LED lights over to your 12V battery, and put the black on ground, then put the other wires on positive, one at a time.
You need to find which wire is the reverse white light, and which wire is the bright red light.
You seem to be missing a wire for the reverse lights.
You also have the yellow wire as Turn Signal, and red wire as Brake, but those are both the bright red, and should be one wire.

Also note that the Cobalt wiring has a rear left turn/brake wire, a rear right turn/brake wire, a front left turn wire, and a front right turn wire.
 
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Tony

Well-Known Member
As Ross said, the turn signal and brake light at the rear are the same "bulb" so to speak - the BCM will control it so that it will flash appropriately whether your brakes are on or not. The rears are shown in the middle of the picture. The unlabeled "B" terminal is the tail light (dim red). On the left is the front turn signals - a completely different circuit. The "B" terminal on those would be a running light, which you obviously won't need to worry about. As far as resistors, the only one I think needs added is on the center stop lamp in order to make cruise control work. I'm not familiar with that, as I haven't done it yet - I only just got my cruise switches wired up, so I haven't tested to see if it works or not yet. The rest don't need resistors - I haven't gotten any bulb out warnings, and the BCM controls the flash, so no "hyperflash" issues.
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I have a good amount of wiring info in my build thread if you feel like sorting through it, as I also didn't get the kit headlights, taillights, or turn signals, so we're a similar boat on that. I just have been going a little nuts on the headlights, so front end stuff is fresh in my mind.
 

OptimizePrime

Goblin Guru
Thanks guys! Ross you're correct I'm currently missing an integrated reverse light - I'm going to add that separately.

I was speaking with Lonny about something unrelated and brought this up - he had a moment of brilliance and mentioned I should tie into the sideview mirrors for the rear turn signals and the CHMSL (third brake light) for the brakes, parking lights and reverse would come from the normal rear harness wires. This would effectively bypass the yellow (driver side) and green (passenger side) brake / turn signal wire.

I tried a Silvania 6ohm 'load balancer' / resistor from autozone on the chmsl that was not plugged into a light and couldn't get the brakes to turn on. I wired this with one end of the resistor to the CHMSL (light blue wire) and one end to the drivers side ground. I don't think the 6ohm resistor is bringing the voltage low enough based on the link below, and will return it and try an 8ohm resistor in the same fashion. Do I have to have a light plugged in? With a light plugged into the chmsl, I would assume a 6ohm resistor would work.


(more chmsl info: https://dfkitcar.com/forum/index.php?threads/chmsl-wiring.714/#post-11389 )
 
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Lonny

Administrator
Staff member
If your running different brake lights from the ones we supply that separate the turn and brake lights you will need to tie into your front turn signal light wires. They are green wires that attach to the mirrors.

For the brakes you will need to split the light blue CHMSL wire and run one to each brake light.

If you plan on using cruise control you may need to install a resistor to ground. The LED lights by themselves may not pull enough of a load to activate the cruise control.


20200212_113141.jpg


Load resistor
Load resistor.jpg
 

Tony

Well-Known Member
Sorry, I misunderstood that the actual lights you're using do have separate circuits for turn and brake. In that case, what Lonny illustrated would work, or you could just not use the turn circuit and wire the brake circuit as factory. I don't know what the actual light itself looks like, so I don't know if that would look weird, but it would save the extra complexity I'd think.
 

OptimizePrime

Goblin Guru
Thanks for the help guys, the problem I'm facing with the CHMSL is that it's a constant 7.5v without the brakes pressed which is enough to turn the LEDs on (so they're on all the time).

Edit: Looks like without the actual 3rd Brake light to draw the voltage <1v and turn out the LEDs, it'll sit at 7.5v. So, if one wants to keep their third brake light, an Impala light works best and then you can run lines to your brakes. If don't want a third brake light and you want to run your brakes off of the CHMSL you must wire in a 100ohm resistor.

The resistor is only for enabling cruise control and not impacting the brake lights.

 
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bradr

Well-Known Member
If you plan on using cruise control you may need to install a resistor to ground. The LED lights by themselves may not pull enough of a load to activate the cruise control.
Oddball side note - my brake light output was not working when firing stuff up on the bench. Net result is for donors with the 3 wire brake switch, it has to be in a "normal" resting position when the BCM is powered up, otherwise it will not work at all. When the switch is not installed on the brake pedal box, the spring causes the switch to go to the "fully pressed" position. Hopefully this will help someone someday.
 
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Briann1177

Goblin Guru
I wanted to add some clarity to this comment. For newer donors that use the 3 wire brake switch (technically a variable resistor), no resistor is needed to maintain cruise (with or without a 3rd brake light). These BCMs drive a relay in the fuse box to drive the CHMSL.
That's what I thought too. However, my cruise control will NOT work work if I unplug my CHMSL. I've tried it. I have an '09.
 

bradr

Well-Known Member
That's what I thought too. However, my cruise control will NOT work work if I unplug my CHMSL. I've tried it. I have an '09.
Ahh, found my mistake. The PCM is what handles cruise, not the BCM. The PCM is tapped in after the relay, explaining what you are seeing. Thanks for the info!!
 

OptimizePrime

Goblin Guru
To close the loop on some issues regarding LED tails on the Goblin after a lot of expletives and countless hours:

1. I kept my turn signal stalk and mounted it under the hood behind the gauges out of sight, this allows me to toggle between autolights on & off ... this is important. You'll probably need to also if you have manual steering

2. You need to plug in the ambient light sensor for any consistency. Small white plug by the cluster gauges

3. Rear taillight turn signals come from the sideview mirror signal.

4. Rear taillight parking signal comes from headlight ON signal -- should / could be wired with a resistor (I used 100ohm) so it's not as bright as your brakes (depends on how your taillights are setup). This is the only wire I have a resistor on.

5. Brake signal wired to stock Goblin brake signal with no resistor.

6. I gave up on cruise control ¯\_(ツ)_/¯

** if your brake signals turn on and off intermittently with no consistency, check your brake switch as it's likely too tight. This switch is very sensitive - mine is installed rather loose.
 
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bradr

Well-Known Member
As an update, I found that a 24 ohm resistor works well. The nice part is they draw MUCH less current (1/4th) than the 6 ohm resistor and generate less heat. Not critical for most, but helpful for my custom setup.
 

Ark :D

Goblin Guru
So I need to bump this thread to make sure I am understanding this all correctly.

My wing acts as a third brake light, but obviously it's not a direct replacement for the Cobalt's CHMSL. But I do want my cruise control to work.

First things first: I see that the ECM controls the output to the light blue CHMSL wire. According to Alldatadiy, that appears to be pin 52 on ECM X2. Am I correct on that?

It sounds like, in order to enable cruise control functionality, I would need to wire a 100 ohm resistor (or is it 24 ohm?) in parallel and send that to ground so the circuit is complete at all times. Then I would wire my third brake light off the light blue wire BEFORE the resistor. The presence of the resistor and the load created by it on the circuit would then cause the light blue wire to carry close to 0v when the light should not be on, and close to 12v when the light should be on, while also enabling the cruise control to work again.

Does that all sound accurate?
 
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Ark :D

Goblin Guru
Just wanting to confirm for everyone that this IS exactly how it works.

If you intend to use a third-party CHMSL (third brake) light, you must run the light blue wire to a junction. One path of that junction should go to the positive input on your CHMSL, and the other path should run to a 100 ohm resistor, then continue on to ground.

If you DON'T intend to use a CHMSL, then you can just run the light blue wire to a 100 ohm resistor, then on to ground.

Since my car isn't on the road yet, I can't confirm that my cruise control works, but I can say that I saw exactly what I expected to see on the light blue wire: without any resistor, the wire carried 7.5v any time the ignition was on. Once I added a resistor and ground connection, the light blue wire carried nearly 0v without the brake pedal applied, and 12v (BEFORE the resistor) with the brake pedal applied.

Hopefully this helps anyone in the future that desires to have a third-party CHMSL with functional cruise control.
 

Torchandregdoc

Goblin Guru
Just wanting to confirm for everyone that this IS exactly how it works.

If you intend to use a third-party CHMSL (third brake) light, you must run the light blue wire to a junction. One path of that junction should go to the positive input on your CHMSL, and the other path should run to a 100 ohm resistor, then continue on to ground.

If you DON'T intend to use a CHMSL, then you can just run the light blue wire to a 100 ohm resistor, then on to ground.

Since my car isn't on the road yet, I can't confirm that my cruise control works, but I can say that I saw exactly what I expected to see on the light blue wire: without any resistor, the wire carried 7.5v any time the ignition was on. Once I added a resistor and ground connection, the light blue wire carried nearly 0v without the brake pedal applied, and 12v (BEFORE the resistor) with the brake pedal applied.

Hopefully this helps anyone in the future that desires to have a third-party CHMSL with functional cruise control.
I've got a bunch of weird brake light symptoms. I'm using the same tail lights as you are. How many watts is the 100 ohm resistor you are using?
 

Ark :D

Goblin Guru
Unfortunately, I am still waiting on the replacement control box for my wing lighting so I have not connected anything permanently yet, so I still have a loose light blue wire carrying 7.5v with ignition on, and no resistor/wire to ground. I was waiting for that box to arrive to permanently finish up that wiring.

*edit* To actually try to answer your question though, it's not a big one.
P = V² / Ω
P = (12)² / 100
P = 144 / 100
P = 1.44W
 
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Torchandregdoc

Goblin Guru
Unfortunately, I am still waiting on the replacement control box for my wing lighting so I have not connected anything permanently yet, so I still have a loose light blue wire carrying 7.5v with ignition on, and no resistor/wire to ground. I was waiting for that box to arrive to permanently finish up that wiring.

*edit* To actually try to answer your question though, it's not a big one.
P = V² / Ω
P = (12)² / 100
P = 144 / 100
P = 1.44W
Ark, thanks for the reply. Let me preface this with the disclaimer that I am electrically ignorant. I've used W=(V)(A) since high school physics and that's where my understanding slows significantly, other than the last 2 days.

Can I ask, where did the 100ohm number come from for this taillight hack. It's all over the web, but I'm super confused. Lonny posted a pic of a resistor above at some point, which confuses me even more. It shows a 12V 50W6RJ

Per the formula I just learned from you,... Lonny, and most of the internets, resistor is a 12V 50W, which would make it .3ish ohms, however, the part number would indicate 6ohm. So, where does the 100 ohm come from that so many people say we should use. It seems much higher.

Also, just so I make sure I understand, the resistor is not changing the voltage to the blue wire, it is just adding load so that the BCM drops the voltage to the blue wire, right?

My brake lights are on any time I'm in gear(auto trans). My brake pedal sensor does not activate the brake lights. My rear and turn signals function, but flash fairly quickly. I'm hoping I just need a few resistors strategically placed. I'm just trying to figure this out with numbers rather than throwing money at the problem with trial and error.
 

Ark :D

Goblin Guru
I'll do my best to help you, but this may be a case of the blind leading the blind. :) If any electrical experts can add anything, please do.

I wouldn't classify this as a "taillight hack". I think what is going on here is, the powered CHMSL wire carries a load while the ignition is on, and the ECM expects to see a certain resistance load on that wire, presented by the stock CHMSL. To be clear here, I think the CHMSL is designed to add resistance to the circuit and ground it, so not just a normal "light bulb" so to speak. I got the 100-ohm number from a thread on here, but I wasn't confident it was right, so I grabbed a 100-ohm resistor and tested it.

Without any resistance load on the light blue wire, it was carrying 7.5v anytime the ignition was on (Tested via 20v setting on my multimeter, touching the positive probe to the light blue wire and the negative probe to ground). Then I shaved some of the jacket off the light blue wire, connected the 100-ohm resistor to that bare spot, and ran the other end of the resistor to ground. Then I again tested with the 20v setting on my multimeter, and at the end of the light blue wire (as in, AHEAD of the resistor in the circuit, not after it), I saw the more-expected outcome: nearly 0v without the brake pedal applied, and a full 12v with the pedal applied.

So in other words, I think there's logic in the ECM that tests for a load on the CHMSL power wire, and that the stock CHMSL provides somewhere around 100 ohms of resistance. Since the ECM "sees" the resistance, it functions normally (enables cruise control and sends the proper voltage through the CHMSL wire). I do NOT feel that the resistor is changing the voltage on the wire via electrical formula, or however you want to say it. I hope that makes sense.

I used the formula I did above, because we don't know the current (amps) going through the wire. It can't be much, but we don't know it, nonetheless. You can find the Power by squaring the Voltage, then dividing that by the Resistance. So 12 volts squared, over 100 ohms. 144/100 = 1.44W, so you would need a resistor that can handle that plus a little more. Since I suspect the resistor I used to test was not rated for that much, I ordered some 2-watt, 100-ohm resistors off Amazon. I'll only need one, and a pack of 100 of them is incoming, so I'd be happy to send you one via snail mail if you want it.

As for the brake lights being on while in gear ... how do they behave when you're NOT in gear?
 
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