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Old 08-19-2019, 11:29 PM   #1
Windsor14STI
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Default How to correctly replace high beam/DRL with LED in factory housing

This is my first post on the forum other than the responses I made to be able to post this thread. I hoped it might be helpful to some folks as I lurked on this forum and couldn't really find anything that helped me. To be honest there was some trial and error with this process and I lost motivation to keep snapping pictures the whole way through, but here goes.

A common question I found, but limited answers to was how to replace the high beam bulbs and still retain DRL capabilities without blinding people, hopefully you will find my installation below helpful.

Let me warn you all by stating there is a noticeable difference between DRL mode and high beam brightness, but the DRLs are still very bright.

To start with you need a bulb that has a DRL mode. Some brands offer this feature through PWM (Pulse width modulation), which is not what you want for a Subaru which just uses a simple resistor to dim the factory halogen bulbs. This resistor (2008-2014) has a 1.13 OHM value (I found this via another thread on this forum with no source information and verified with a multi meter and some Math).

The "bulbs" I chose (2014 STI) were the 9005 2STROKE 2.0 by Morimoto 2STROKE 2.0 by Morimoto, they claimed a DRL mode between 4V and 9V DC and to operate between 6 and 18V DC. To me this meant my voltage goal was between 6V and 9 V DC which would be in both the DRL mode range and the operating range. Also, as a side note you DO NOT need the anti-flicker harness. Here are the specs snipped from the web page linked above:


Now here comes the nitty gritty, I won't bore everyone with the Math and Ohm's law stuff, but here are the basics. Essentially in the DRL circuit the are 3 major voltage drops. 1 across the DRL resistor, and 1 (in parallel) across each headlight bulb. The sum of these drops equals the input voltage to the system, in other words the voltage when the car is running, my car tends to be 14-14.6 VDC (I tested with fan blasting, heated seats, rear defrost to see how low it would go).

When you change out your inefficient halogen bulbs for LEDs you will be drawing much less current and therefore the voltage drop across the factory 1.13 OHM resistor will be much less (V=IR).

Therefore in order to get our voltage down to the specified range for the LED we need a new DRL resistor with the correct value.

Here is the bottom line and where some trial and error frustration came in. The LED replacement bulbs do not behave like a linear resistor, so instead of taking you through the Math I will just give the solution.

You will need a 4 OHM, 50W or greater resistor. There are 2 major kinds available at reasonable prices, for $5 or less you can get an axial lead power resistor or for about $10 one with a pigtail. Here is a picture for comparison:


I will risk confusion by doing this, below is a link to the resistor I ended up using in my final set up. The pictures I have are for putting together the axial resistor that I first used with the incorrect value. When I got the correct value resistor in, I redid the work without photos (sorry).

Purchased resistor part LPR100 4R J : https://www.mouser.com/ProductDetail...rrencycode=USD

Axial Style that will work part THS503R9J : https://www.mouser.com/ProductDetail...rrencycode=USD

First, for a clean install you will need to get a used DRL resistor WITH CONNECTOR off of EBAY, I think the connectors from 2006-2019 are all the same (please double check 2015+ guys and gals). I got a 2007 STI resistor with connector for just over $8.00. Once you have this cut it as close to the resistor as possible and toss the resistor, keep your connector and pigtail. For those who do not know the factory resistor and connection we will be using is located under the passenger side headlight housing. You will probably want to take your airbox out to access it.


Skip this if you purchased a resistor with a pre-made pigtail. For axial resistor solder 2 leads to each side of the resistor about 8-10 inches long. I just used looped my wire (14 AWG) through the leads and used solder sleeves. After this shrink tube over connections (I used 1/4" diameter shrink tube). Here are a series of pictures:






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Last edited by Windsor14STI; 08-19-2019 at 11:35 PM.
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Old 08-19-2019, 11:30 PM   #2
Windsor14STI
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Once this is complete, use 5/16" diameter tubing to hold the leads together:



Now slide another 5/16" diamter piece over the one you just shrunk:


If you bought a resistor with pre-made pigtail resume here. Splice your EBAY connector leads to your resistor (I chose solder sleeves), and slide your shrink tubing down over them and shrink it (don't have to cover them, but it looks better).





And now you have your very own resistor harness:


To finish the job simply, mount your resistor, preferably where the heat from the engine isn't too prevalent (in the vicinity of the stock one) and unplug the factory resistor and plug your new one in. Changing back to stock is no problem, simply unplug yours and plug the stock one back in.

Not that you can tell much from these, but here are some pics DRL vs high beam:



Hope this helps someone.

-Windsor14STI

Last edited by Windsor14STI; 08-19-2019 at 11:37 PM.
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Old 08-20-2019, 09:20 AM   #3
puffer
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Thank you for a nice write up.

Do you have any suggestions as to what LED might be better suited to replace OEM halogen bulbs with respect to beam optics, i.e. argument that LED bulbs might not work correctly in the halogen headlight since the light source is not in the same place.
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Old 08-20-2019, 11:38 AM   #4
Gally316
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Nice write up. We need more current tech info like this.
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Old 08-20-2019, 07:03 PM   #5
Windsor14STI
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Quote:
Originally Posted by puffer View Post
Thank you for a nice write up.

Do you have any suggestions as to what LED might be better suited to replace OEM halogen bulbs with respect to beam optics, i.e. argument that LED bulbs might not work correctly in the halogen headlight since the light source is not in the same place.
Thank you both for the friendly feedback. As far as the beam pattern I am not an expert by any means, but the Morimotos have a great pattern, in my opinion, and are a definite improvement in brightness and visibility over stock (Drove with them at night through a rainstorm recently). The other brand that I considered was Diode Dynamics. They appeared to have done extensive research into the beam pattern, but the DRL mode worked via pulse width modulation and would not have worked with the system in our cars.

There is a youtube channel called Headlight Revolution that I checked out and has beam patterns for many bulbs you may be interested in. I would advise checking them out and seeing what you like.

Here is a link to the Morimoto video:

Here is a link to the main channel page: https://www.youtube.com/channel/UCv0...UNFWYDsf_t9fqQ
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Old 08-21-2019, 05:37 PM   #6
car_freak85
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I'd just like to point out that the bulb reflectors in a halogen lamp will never properly reflect and aim the light produced by any HID or LED plug'n'play bulb. That is all, carry on.
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Old 08-22-2019, 12:04 PM   #7
BajaTim
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Quote:
Originally Posted by car_freak85 View Post
I'd just like to point out that the bulb reflectors in a halogen lamp will never properly reflect and aim the light produced by any HID or LED plug'n'play bulb. That is all, carry on.


Have you been to the Headlight revolution site and looked at their filmed actual examples? They often use 3-4 different models to illustrate the difference between halogen and LED. The “aiming” looks pretty similar to me for their recommended brands (identical in fact - only the brightness differs).
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Old 01-04-2021, 02:07 AM   #8
ilarson007
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Well, it's too bad the photos are gone, but I figured out what I needed anyway. Thanks!
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