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2003 Volkswagen Passat GLS Manual 1.8L
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Discussion Starter · #1 ·
I went to the car and popped in some LED's for the front blinker bulb, and I got nothing. I know its probably because the voltage is so low that the computer thinks its a blown bulb, which would require resistors but I wanted to ask around in case one of you peeps have already done this.

LED's seemed like a no brainer, when I saw a pair of amber ones that fit the Passat at AutoZone I said heck yes. LED's look so good I'm obsessed. I also want to know if LED's are possible for the reverse and side marker lights too.
 

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Incandescent lights look like a resistor to the car's 12V supply. LED's require a specific amount of current to work. I would assume that any LED light that you buy for a car would have the appropriate circuitry to make them work with the 12V in the car.

LED's are diodes and so are directional. They have a + and - side and only work when installed in the correct orientation.

Try switching the lights' terminals (put them in the other way) to see if that helps. If not, you can test them by connecting them to the 12V battery in the car with alligator clips or something similar.
 

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Well, some good news:
Unless you have the bulb-out monitor (which, IIRC, was only on the W8 cars here in the US), there's no 'computer' for the exterior lights. Just simple dumb switches.
LED away on the exterior lights. I am currently running LEDs for:
--Repeater lamps
--'City' lights
--Reverse lamps
--Brake/tail lamps
No malfunctions due to this, except for a funky AM radio interference issue when reverse is selected. IIRC, this didn't happen until I went LED for the reverse lamps (which, IIRC, was after the rear-view camera and rear parking sensors were installed.)

As Iowegian said, if the bulb doesn't work, take it out, rotate 180*, and reinstall.

Turn signals, those are a little tricky, though. Because an LED has so little current consumption, they WILL make the turn/hazard flasher relay (which is integral to the hazard switch) react as if a bulb had blown - it'll flash at 2x speed.
LEDs in the repeater lamps (the small turn signals on the fenders) will go un-noticed; going LED on the front and/or rear turn signals will require either adding load resistors to the circuits (clunky), or modifying the hazard switch (writeups exist here - somewhere.)
 

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Discussion Starter · #4 ·
Well, some good news:
Unless you have the bulb-out monitor (which, IIRC, was only on the W8 cars here in the US), there's no 'computer' for the exterior lights. Just simple dumb switches.
LED away on the exterior lights. I am currently running LEDs for:
--Repeater lamps
--'City' lights
--Reverse lamps
--Brake/tail lamps
No malfunctions due to this, except for a funky AM radio interference issue when reverse is selected. IIRC, this didn't happen until I went LED for the reverse lamps (which, IIRC, was after the rear-view camera and rear parking sensors were installed.)

As Iowegian said, if the bulb doesn't work, take it out, rotate 180*, and reinstall.

Turn signals, those are a little tricky, though. Because an LED has so little current consumption, they WILL make the turn/hazard flasher relay (which is integral to the hazard switch) react as if a bulb had blown - it'll flash at 2x speed.
LEDs in the repeater lamps (the small turn signals on the fenders) will go un-noticed; going LED on the front and/or rear turn signals will require either adding load resistors to the circuits (clunky), or modifying the hazard switch (writeups exist here - somewhere.)
Thank you both for helping me understand this better. lowegian, you helped me see its current that I’m talking about not voltage. And I would’ve never thought to check if I didn’t have a bulb out sensor
 

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Discussion Starter · #5 ·
Incandescent lights look like a resistor to the car's 12V supply. LED's require a specific amount of current to work. I would assume that any LED light that you buy for a car would have the appropriate circuitry to make them work with the 12V in the car.

LED's are diodes and so are directional. They have a + and - side and only work when installed in the correct orientation.

Try switching the lights' terminals (put them in the other way) to see if that helps. If not, you can test them by connecting them to the 12V battery in the car with alligator clips or something similar.
Thank you lowegian!
 

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Incandescent lights look like a resistor to the car's 12V supply. LED's require a specific amount of current to work.
Additionally, incandescent bulbs act like variable resistors; resistance goes up with filament temperature. LED don't require a specific current to turn on, rather a specific Voltage; the "turn-on Voltage" for Red LEDs is less than 2V, but increases as the LED colors go from Orange-Yellow-Green, then to Blue. Unlike incandescent, LED color remains constant despite the brightness changing with current.
 

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It looks like there are replacement relays that can be used for the turn signals to prevent the fast-flashing turn signal syndrome. I'd check into those if you have problems. I don't know if a drop-in replacement is made for the VW Passat but if you can find one, that would be the best solution, IMO.

The reverse and side marker lights shouldn't have any issues if they are quality parts.
 

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Somewhere on this site there is a definitive list, with reference to converting each and every bulb to LED and any other needed parts/devices to make them all work properly.

ECS Tuning also used to have a complete conversion kit to LED. I don't know if that is still available on their site. It also had a list of every bulb location and the conversion to the proper LED bulb number.

This was all a few years back though.
 

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You can modify the existing hazard switch with a different resistor. I did. Trying to find the pics now. It was a pain in the ass, though.

edit: Towards the end of my rehab thread.
 
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Somewhere on this site there is a definitive list, with reference to converting each and every bulb to LED and any other needed parts/devices to make them all work properly.

ECS Tuning also used to have a complete conversion kit to LED. I don't know if that is still available on their site. It also had a list of every bulb location and the conversion to the proper LED bulb number.

This was all a few years back though.
I replaced all of my bulbs, at least the ones that were accessible, with LEDs. These fit right in, just watch polarity, and get the ones designated with "CANBUS", you won't get bulb error messages.
 

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The only motivation I would have for switching from incandescent to LED would be for color. My A5 doesn't have anything other than LEDs, as far as I know. And it's interior lights are blue-white like fluorescent, which if a Tungsten filament would burn out in seconds.
 
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