New LED Tail Light

WORBC

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I recently installed new LED tail lights and now, every 10 mins or so, I get a flashing glow plug light (as noted in many posts on this board). It appears to be caused because the LED lights have a lower resistance than the OEM lights.

I haven't installed a resistor in parallel or anything yet, my question is as a new VAG COM user (I hae software, dongal, and computer), is there a way I can just turn on this "lights status checking"?

thanks,

--terry
 

daedalus

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I don't have LEDs so I am far from an expert. That being said, you said the LED resistance is too low, causing the problem. Putting a resistor in parallel with the LED would lower resistance, making it worse. A Series resistor would increase circuit resistance.
 

WORBC

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daedalus said:
I don't have LEDs so I am far from an expert. That being said, you said the LED resistance is too low, causing the problem. Putting a resistor in parallel with the LED would lower resistance, making it worse. A Series resistor would increase circuit resistance.
Hummm. That's a very good point. I need to reread the threads that I hae have found, they all have suggested a resistor to be placed in Parallel. Heck, if you do a search on google for LED lights and CEL, there are some posts that recommend the same thing, but you are right, that would just lower the resistance where putting one in series, a low ohm resistor, would might work.

--terry
 

GoFaster

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You need to increase the *current* drawn by the LED lamps. This means the resistor has to go in *parallel* as you originally stated.

Bulb monitoring enable/disable is a Mk5 thing; can't be changed on your Mk4 car.
 

Nutsnbolts

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The LEDs will only throw the GPL when they are installed in the brake light positions. As stated, the LED resistance is too high, and the ECM thinks that the bulbs are burned out. I'm hoping to have a legitimate fix for this by May. Stay tuned...

-Rich
 

JetPuf

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WORBC said:
I recently installed new LED tail lights and now, every 10 mins or so, I get a flashing glow plug light (as noted in many posts on this board). It appears to be caused because the LED lights have a lower resistance than the OEM lights.

I haven't installed a resistor in parallel or anything yet, my question is as a new VAG COM user (I hae software, dongal, and computer), is there a way I can just turn on this "lights status checking"?

thanks,

--terry
Which LED tails did you install? I've seen several available. were they complete housings and everything, or just bulb inserts?
 

WORBC

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JetPuf said:
Which LED tails did you install? I've seen several available. were they complete housings and everything, or just bulb inserts?
They are complete enclosures and are great; I really like them, except for this minor irritation.
If it’s the resistance problem and a resistor is inserted in parallel, then the resister will only be used when the brake pedal is not pressed to increase the resistance sense by the computer. Once you press the break light, then all current will flow through the lights as current will follow the path of least resistance correct?

Rich, (Nutsnbolts) what are you doing to fix this? Can I help?


--terry
 

Nutsnbolts

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Terry:

The resistor (also known as a ballast or ballast resistor- if you're a Chrysler driver, the name will sound familiar), when mounted in parallel, will always have current flowing through it, even when you are applying the brake. You are correct that electricity will follow the path of least resistance, but not when things are wired in parallel. In parallel, the circuit supplying power, in this case coming from the brake light switch, acts as a manifold would in a car, and supplies each parallel component with the same amount of voltage, in this case, 12V. This means that while the LEDs are happily consuming fractions of an amp due to their high resistance, the ballast is allowing oodles of amps through to ground.

One of the main reasons that I switched to the LEDs (other than never having to go back there and wrinkle my hand trying to change bulbs:) ) was to reduce overall amp draw. This resistor is totally the opposite of what I was going for, since the amp draw hasn't changed one iota except when the running lights are on (that conversion is easy). Here's the plan:

Since no one has found a way to turn off the bulb sensing feature in the ECM on the pre-Mkv, I plan to fool it another way. The ECM only sends a small signal voltage (about 5V I believe) to the rear brake lights when the brakes are not applied to see if the bulbs are present and accounted for. The wire that carries this signal is on the brake light side of the brake switch, and is seperate from the brake light power. When the brake is applied, this signal is interrupted by the 12V current from the brake light switch that is heading for the brake lights. What I am planning to do is send that 5V reference signal through a low-ohm resistor to ground, away from the brake light bulb circuit, so that the signal still goes through they way that it would if the brake lights were there. In between the resistor and ground, I would wire a semiconductor (this is the part that I haven't had time to look up yet) that would interrupt the ground signal when it received the current from the brake light switch, thus making the ECM think that the 12V is there. Since the semicondictors are high resistance (even more than the LEDs), very little current would be consumed while the brake lights were lit, and the end result would be the same- no GP light. The only piece of the puzzle that I need is the name of the semiconductor (MOSFET?) Instead of amplifying the signal like a transistor, it interrupts it. I used to know what these were called. Once I get that, and figure out how to use it (which should be pretty easy), I'll get it wired in the car and start a new thread.

I also plan on modifying my blinker so that it still blinks at the correct speed with the LEDs installed. Right now, I have TWO MORE ballasts installed, one for each side, to make them work. I'd like to get those out of there too.

Let me know if you come up with the correct component name... I'm DYING to do this.

BTW- My house is in Weare! My wife and I are in KS while I'm in school for the next few years, but I hope to get back there when I get out. If home is where the heart is, I never left NH! :)

-Rich
 
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WORBC

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Nutsnbolts said:
Terry:

.....The only piece of the puzzle that I need is the name of the semiconductor (MOSFET?) Instead of amplifying the signal like a transistor, it interrupts it. I used to know what these were called. Once I get that, and figure out how to use it (which should be pretty easy), I'll get it wired in the car and start a new thread.

I also plan on modifying my blinker so that it still blinks at the correct speed with the LEDs installed. Right now, I have TWO MORE ballasts installed, one for each side, to make them work. I'd like to get those out of there too.

Let me know if you come up with the correct component name... I'm DYING to do this.

BTW- My house is in Weare! My wife and I are in KS while I'm in school for the next few years, but I hope to get back there when I get out. If home is where the heart is, I never left NH! :)

-Rich
Rich, what schooling are you attending? I'm up here temp while I'm in school as well...

Thanks, this helps; the piece that you are talking about is more like a voltage sensing switch than anything else, isn't it, maybe a diode? With certain specialized diode, the side (leg) that has the highest voltage “pushes” the voltage and shunts the other side off.

The “switch” or diode will have 5v on one side and will connect to the return on the light side and act like a short while no voltage is applied. However, once the 12V is applied to the "return side" the switch will sense the +12V and shunt the 5v ("bias" lighting the brake lights? Full wave rectifiers do this sort of thing change AC to DC.

I've seen this circuit somewhere, but can't remember.

What size (ohms and watts) are your ballast resisters so that I can get some installed for the time being and stop the annoying flashing glow plug light?

--terry
"Live Free or Die"
 

WORBC

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It is a diode! Put +5V on the annode and the +12V on the cathode. As long as the 12V is not preseant the diode will allow the "switch" operation and you will get 4.3V out the cathode (.7v voltage drop across the PN junction). When the 12V appears the PN junction will close and the shunt the 5v.

I wonder if the Diode will work just jumping from the pos to neg wires connecting directly before the light on the wires, having the negitive side connect to the annode and the +12V from the break swithc connect to the Cathode?

--terry
 

Nutsnbolts

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Terry:

Have a look at this... It is the circuit that I propose.


I need to know the name of that component, and then we can wire it up and see what happens... I've got to check the Bentley as well to get the exact color for the 5V signal wire so that I know what I'm looking at under there.

I'm going to school here for auto restoration, but auto electrical systems and diesel engines are my forte...

-Rich
 

WORBC

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Nutsnbolts said:
Terry:

Have a look at this... It is the circuit that I propose.


I need to know the name of that component, and then we can wire it up and see what happens... I've got to check the Bentley as well to get the exact color for the 5V signal wire so that I know what I'm looking at under there.

I'm going to school here for auto restoration, but auto electrical systems and diesel engines are my forte...

-Rich
Kewl, this makes since, let me know what i can do to help.

What size (ohms and watts) are your current ballast resisters?
 

Nutsnbolts

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You'll love this- I used 4 ballast resistors from a Chrysler ignition system- I wired them in series, for about 6 ohms total, and use one pair of the ballast resistors for each side. I think it cost about $20 for all four. I also use the second side of the large ballast for the blinker circuit...

-Rich
 

WORBC

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Kinda hijacking this thread and talking more about the LED tails than VAG Com, but rittle me this batman. Ever since installing my LEDs,, my cruse control had stopped functioning, however, I had the Stealership install a new bracklight switch as per the recall notice. SO today I put the OEM tails back in and sure enough, the cruse control started working normal again. Any ideas?

Also, I stopped by the local radio shack and got some 10W, 10ohm resistors, as well as some 10W, 6ohm, and i'll try this this weekend, if I pop a fuse, I know they don't work.

I could handle the flashing glow plug light every once in a while, but I really need that cruse control. Any suggestions?

--terry
 

weasel

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I bet you just need to up your ballast resistors. My guess is that the cruise control system is "seeing" inadequate resistance for your brake lights and thinks that there is a problem with either the bulbs or the switch.
 

WORBC

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weasel said:
I bet you just need to up your ballast resistors. My guess is that the cruise control system is "seeing" inadequate resistance for your brake lights and thinks that there is a problem with either the bulbs or the switch.
Weasey, I don't have any ballast resistors installed yet, I just got some today. Do you have any installed? If so, what resistance and wattage? If you have a source that would be very helpful.

thanks,

--terry
 

Nutsnbolts

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According to the Bentley, T121/22 (pin 22 out of the ECM 121 pin plug), a red wire with a black tracer, should be what supplies the 5V(?) reference signal. From there, it merges at connector A18, with the wire that comes out of the brake light switch and heads to the brake lights. The cruise control circuitry is handled by a completely different part of the brake light switch. What we're seeing is the ECM losing the ground for the reference signal since the LEDs are such high resistance. As a result, the ECM shuts the cruise down in case there is a problem with the switch (which it should be able to figure out if the cruise side and the light side agree, but it may not be that sophisticated). Sooooo, if I ground T121/22, and apply the 12V to it when the brakes are lit, then I should be able to get around this dilemma. I can do this with a relay pretty easily... Check it out:


When the relay is NOT energized, the reference signal is sent from the C, or common contact, to the NC or normally closed contact, to ground. When the relay is energized by the 12V brake light signal, the C or common contact swings over to the NO or normally open contact and 12V is sent to the ECM back through the T121/22 wire to tell it that the brake lights are lit.

Does everybody get this?

I'll have to pick up a relay at Radio Shack and test this theory, unless some other guinea pig beats me to the punch...

-Rich

PS: ADMIN... Can we move this thread over to the upgrades/non TDI section? I think it belongs over there...
 
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weasel

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I knew it had something to do with the bulbs, just forgot what ... and no I don't have resistors. Have't got led's yet.
 

2004STARWARSTDI

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Was wondering what the life expectancy of the LEDs are.:confused: Some of the vehicles at work have LEDs and some have bulbs. The LEDs are slowly burning out! :eek: Not too impressed with them so far.
 

Uwe

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Hmm, in priciple LEDs should last 50,000 hours or more. This assumes they are quality parts and not driven harder than they are rated. 50,000 hours a heck of a long time (over 5 years of continuous use), several times the expected life of a car.

-Uwe-
 

WORBC

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Nutsnbolts said:
According to the Bentley, T121/22 (pin 22 out of the ECM 121 pin plug), a red wire with a black tracer, should be what supplies the 5V(?) reference signal. From there, it merges at connector A18, with the wire that comes out of the brake light switch and heads to the brake lights. The cruise control circuitry is handled by a completely different part of the brake light switch. What we're seeing is the ECM losing the ground for the reference signal since the LEDs are such high resistance. As a result, the ECM shuts the cruise down in case there is a problem with the switch (which it should be able to figure out if the cruise side and the light side agree, but it may not be that sophisticated). Sooooo, if I ground T121/22, and apply the 12V to it when the brakes are lit, then I should be able to get around this dilemma. I can do this with a relay pretty easily... Check it out:


When the relay is NOT energized, the reference signal is sent from the C, or common contact, to the NC or normally closed contact, to ground. When the relay is energized by the 12V brake light signal, the C or common contact swings over to the NO or normally open contact and 12V is sent to the ECM back through the T121/22 wire to tell it that the brake lights are lit.

Does everybody get this?
Rich, this makes sense, when can you try it out? I can pick up a relay tomorrow and, build this circuit and try it Friday. I've got a Bentley book and other schematics so I will try and locate these wires, but if you can give me some locations, then it will be easier.
 

unitacx

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(messages consolidated)
weasel said:
I bet you just need to up your ballast resistors. My guess is that the cruise control system is "seeing" inadequate resistance for your brake lights and thinks that there is a problem with either the bulbs or the switch.
It's simpler than that. The cruise must ground through the brake light, which is how it disengages. If either the LED doesn't ground effectively, or more likely the immo is applying a voltage across the brake light circuit, the cruise won't go to ground.
WORBC said:
[The threads] all have suggested a resistor to be placed in Parallel.
That means that the issue is one of too high resistance, which is the idea of LED lights (less current).
I have a set of LED tail lights, 1156 (supposedly brake lights, but about the illumination power of taillights) and the only problem was that I needed to cut the plastic shield intended to Murphy-proof the taillight from installation of (real) brake light bulbs. IIRC, there is a VAG-COM adjustment for this, but I hadn't run into an issue with these lights.
Nutsnbolts said:
When the relay is NOT energized, the reference signal is sent from the C, or common contact, to the ...
It seems that the cause is more related to the "off" status of the LED (a reverse connected diode). The LED is an open circuit until the 12v breakdown voltage is applied. This is also called the threshold voltage and avalanche voltage, explained very succinctly at http://britneyspears.ac/physics/pn/pnjunct.htm
According to Britney, either a 3 watt light in parallel with the brake light or a 50 ohm resister to either the reverse lights or to the trunk light will work better than the relay. All you need to do is ground the small signal from the ECU and cruise control -- something the LED does not do.

NOTE: The 1200 ohm resistor to ground described by Mike Morriss below, seems to be a more elegant solution. The idea is to bleed off the voltage which the LED does not do. (typically 5 volts, but it's hard to say for sure)


- stan
'00 Golf (Rocketchip II, 520, TT 17 wheels, Valeo E-codes)
'81 W123 240D/300Dt 5 sp
 
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Nutsnbolts

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Worc:

I'm going to be away this weekend, and for a good part of next week, then I'm going to California the 17th for a week. I may not be able to get to it for a couple of weeks, but if you're willing to try it out, I'll help in any way that I can. PM sent...

-Rich
 

wny_pat

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Uwe said:
Hmm, in priciple LEDs should last 50,000 hours or more. This assumes they are quality parts and not driven harder than they are rated. 50,000 hours a heck of a long time (over 5 years of continuous use), several times the expected life of a car.
Truck Lite warranties their sealed LED units for Limited Lifetime. To bad they don't make a unit for our TDIs.
 

Nutsnbolts

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I've had mine in for over 3 years, 3rd shift driving back and forth to work 90 min. each way. I haven't had to replace one in the rear yet! However, the side marker is a different story. Wierd.

-Rich
 

kack

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some help with led tail lights for you

I have had a set of led tails in the getta now for almost a year.
The best fix for the brake light and cruise control circuit was to add an extra 194 light socket with a burnt out bulb on one side only. Its hidden from view in the tail light and provides the easiest solution (no glow plug light flashing either). I did try some other ideas but this one worked the best. You can also add one per side to the turn signals to make them led's as well. I'm going to order some more led's this time to make a complete led lighting setup for all the lights except the fogs and headlights.

btw the high mount brake light is an led strip, so its going to stay lit without the added load of the spare bulb.

If you would like to ask questions post them up here I'll watch this thread
 

WORBC

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kack said:
some help with led tail lights for you

I have had a set of led tails in the getta now for almost a year.
The best fix for the brake light and cruise control circuit was to add an extra 194 light socket with a burnt out bulb on one side only. Its hidden from view in the tail light and provides the easiest solution (no glow plug light flashing either). I did try some other ideas but this one worked the best. You can also add one per side to the turn signals to make them led's as well. I'm going to order some more led's this time to make a complete led lighting setup for all the lights except the fogs and headlights.

btw the high mount brake light is an led strip, so its going to stay lit without the added load of the spare bulb.

If you would like to ask questions post them up here I'll watch this thread
A burnt out bulb? Please explain how this "open" circuit works?

Thanks.

--terry
 

kack

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the burnt out 194 bulb adds the resistance to compensate for the led's
I did use a working bulb at first but it failed and the setup kept working.
I have it connected in parallel on the brake light bulbs wiring on one tail light only. I can take some pics no problem let me know.

 

WORBC

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kack said:
the burnt out 194 bulb adds the resistance to compensate for the led's
I did use a working bulb at first but it failed and the setup kept working.
I have it connected in parallel on the brake light bulbs wiring on one tail light only. I can take some pics no problem let me know.

Kewl, i've been setting here trying to figure out where i can get a bad bulb...:confused: I'll try this tonight. Sounds sound and should do what I need.

--terry
 

WORBC

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kack said:
the burnt out 194 bulb adds the resistance to compensate for the led's
I did use a working bulb at first but it failed and the setup kept working.
I have it connected in parallel on the brake light bulbs wiring on one tail light only. I can take some pics no problem let me know.

Ok, so far, so good -- I installed the LEDs again and after chasing the right wires, brown is ground and red with white stripe is brake hot, I installed the extra light attaching the leads to each of the wires above. Tested it on the road, Cruse Control worked and no flashing glow plug light yet.

If can figure out how to attach photos, I'll put some in here. I have complete install photo.
 
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