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Discussion Starter · #1 ·
Hi everyone,

I searched high and low for a solution to this problem and I have a good idea of what's happening, but can't seem to find a definitive answer for the MK3.


PROBLEM: Fog lights won't light up, all other signs indicate they should.


MODEL: 2014 Hatch Titanium


SCENARIO: I decided to swap out my factory fog light assemblies for LEDs instead. The physical swap was clean and relatively easy. However, as soon as one of the lights went in, the fog lights would no longer turn on. This now also holds true for the original fog light bulbs. Further investigation confirmed that there is no current in either plug. The control switch works, the cluster panel green LED indicator light illuminates, one of the internal relays engages (clicks on/off) corresponding with the switch and green LED, fuse 75 is good (swapped it out with a fresh 15A ATM), and yet there is still no power to the lights themselves.


CURRENT KNOWLEDGE: I have discovered that this problem existed in previous generations (MK2) where a fuse would blow for a relay in the body control module that also happened to control the Fog Lights. This was also the same relay associated with the old parking light/fog light hack. As the MK3s also have a BCM and the symptoms of the problem are identical to the MK2s with the same problem, I was hoping if someone had some insight into the electrical layout of the OEM fog lights.


QUESTION: Does anyone know what other associated fuses the OEM fog lights would be connected to besides the labeled #75 15A fuse? Or, does someone know specifically if there is another issue here? I'm prepared at this point to start pulling fuses if no one has an answer.



Thanks.
 

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Discussion Starter · #4 ·
Yeah I already searched through p.221-228 multiple times. The only indication of a fuse linked to the fog light is #75 behind the glove box. If there is another related fuse, it is not clearly indicated anywhere in the manual (probably since the fogs are optional) and I was hoping someone here may either have a wiring diagram, knowledge of other fuses/relays, or another answer to this specific problem.

I'm ready to start pulling fuses at this point to see if I can come up with something. I'll report back if I do find an answer.
 

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Assuming there are no breaks in the wiring, I would suspect that there is an issue with one of the control boxes like you were thinking. I would prob bring it to the dealer as its still under warranty.
 

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Assuming there are no breaks in the wiring, I would suspect that there is an issue with one of the control boxes like you were thinking. I would prob bring it to the dealer as its still under warranty.
Is it possible there is an inline fuse coming out of the relay box for the lights?
 

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Hi everyone,



I searched high and low for a solution to this problem and I have a good idea of what's happening, but can't seem to find a definitive answer for the MK3.





PROBLEM: Fog lights won't light up, all other signs indicate they should.





MODEL: 2014 Hatch Titanium





SCENARIO: I decided to swap out my factory fog light assemblies for LEDs instead. The physical swap was clean and relatively easy. However, as soon as one of the lights went in, the fog lights would no longer turn on. This now also holds true for the original fog light bulbs. Further investigation confirmed that there is no current in either plug. The control switch works, the cluster panel green LED indicator light illuminates, one of the internal relays engages (clicks on/off) corresponding with the switch and green LED, fuse 75 is good (swapped it out with a fresh 15A ATM), and yet there is still no power to the lights themselves.





CURRENT KNOWLEDGE: I have discovered that this problem existed in previous generations (MK2) where a fuse would blow for a relay in the body control module that also happened to control the Fog Lights. This was also the same relay associated with the old parking light/fog light hack. As the MK3s also have a BCM and the symptoms of the problem are identical to the MK2s with the same problem, I was hoping if someone had some insight into the electrical layout of the OEM fog lights.





QUESTION: Does anyone know what other associated fuses the OEM fog lights would be connected to besides the labeled #75 15A fuse? Or, does someone know specifically if there is another issue here? I'm prepared at this point to start pulling fuses if no one has an answer.







Thanks.


I am 99% sure I have your answer. Did you get an all LED housing?

I was the first in the States to install full LED fogs in an MK3. LED's are reverse polarity. If you plug in an LED tag bulb and it doesn't light up, you remove it and turn the bulb the other way. Same goes for these housings. Unfortunately we cannot turn the bulb or plug around. You can either cut the notches out in the cars plug and flip it around and it will plug in. OR, you will need to get a pic tool and release the pin connectors in the cars plug. Put the positive in the negative hole and the negative where the positive was. Plug into the lamp and they will work. See pics below:







 

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I know that. I am telling him what he did wrong that caused the issue.
 

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I see. I bet he upset some sort of can bus module. I wonder if a battery disconnect, both positive and negative would reset the module.
yeah, maybe a hard reset (disconnected for at least 5 minutes) will help...
 
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