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2018+ STi Fog Light Install. (Using OEM Parts)

20620 Views 33 Replies 11 Participants Last post by  GranTuring
I had a chat with another member about how to install fog lights in a 2018+ STI yesterday. He suggested that others might like that information and I have not seen it posted anywhere so I will give it a go.

If I missed it in my search, I am sorry for repeating the info.

I want to start by apologizing for the lack of in-depth pictures, I did the install almost a year ago and never recorded any of it.
If I can get around to pulling the battery to get better pictures I will update this thread, or if anyone does this and wants to share pictures then by all means go ahead.

This setup will not work with cars with the blind spot monitoring button. Unless you never use the button then you can leave it behind the dash, I would assume.( I don't have it so I can't confirm)
Also the setup will only be able to turn the fog lights on when the low beams are on, just like factory fog lights. Because this is the factory set up, minus the forward harness.

Here is a list of OEM part numbers so members can buy the parts separately. It is cheaper to just buy what you need than buying the WRX Fog Light Kit, since you won't be using the bezels or fog lights ( they are not bright enough to compete with the LED headlights)

Replacement panel with the knockout removed QTY 1 : 83472FJ070VH
Right fog light bezel with no turn signal hole QTY 1 : 57731VA380
Left fog light bezel with no turn signal hole QTY 1 : 57731VA390
Fog Light Relay QTY 1 : 82501AG041
Fog Light Button QTY 1 : H4510FJ000
M6 J nut QTY 4 : 902510032
Bolt FLG 6X21 QTY 4 : 901000171
Harness QTY 2 : 84981VA010 - Not required *
Fog lights in the WRX Kit QTY 2 : 84501AJ060 - Not Required ( IMHO Too dim to use with the LED headlights )

* You don't need the harness from the kit. They are just used to get the connectors that plug into the fog lights to make your own.
I did not list an alternatives because I cannot speak for the quality of an aftermarket connector.
However it may be worth it to some to find a cheaper option since they are like $25 each just to cut the plugs off to wire in.

Full Kit with fog lights and the bezels WITH turn signal holes QTY 1 : H4510VA040

Total cost of individual parts can be had around $130 plus shipping from Heuberger. That is including the factory harnesses and not including the fog lights themselves.( again you don't want them trust me )

I Include the Factory Instructions to install the WRX kit because I did not take pictures. They are pretty straight forward, but we are obviously skipping steps 12, 13, and 14.
This will help get everything installed then I will walk you through how to wire it up.

Once done installing the parts we have to wire the lights.
All the wiring inside the cabin is already in the car, so we just have to worry about under the hood.
The blue power wire from the relay behind the glove box goes through the loom to a brown connector under the fuse holders in the engine fuse box.
It however does not come out of the that connector, so we have to splice that wire and run our new power wires to the fog lights.
Or if someone can source the correct pins we could just crimp them and put them in the correct positions on the connector. ( I was unable to locate them, but admittedly did not look too hard )
If anyone figures this out and wants to share I will add it here.

First we have to remove the battery so we can pull the fuse holder up and out of the box. you can see in my picture later that without removing the battery you cannot get the fuses out far enough to reach the connector.

Second you have to depress these tabs and pull up on the fuse holder to pull it out of the box and over towards the battery tray.

Next we need to unclip the brown through joint connector from the wall of the fuse box. It unclips similar to the fuse holders.
I don't have a picture of it removed or a picture of the pin-out of the connector but I will include a picture of the wiring diagram.

This is the connector and you can see where I spliced the factory blue wire with my two red power wires with the black heat shrink.

Here is the fog light diagrams. The second is not needed for this install but just to have the full diagram in one place.

The blue wire labeled C8 in the first diagram is the wire we need to splice. The wires B22 and B23 are not in the connector coming out of the brown joint connector, so we have to make our own.
This is where if anyone finds the correct pins we could just crimp our wires and put them in the outbound connector.

The bottom of the first diagram has the connector pinout highlighted. Make sure we have a blue wire where it says number 8.
You can check it is the correct wire by checking continuity with a digital multimeter on the pin in the connector with the pin in the relay box behind the glove box.

Once verified we can cut it and splice the wire with our favorite method. Your call on how you do it. I prefer the small open barrel crimp joints, OEMs use them so they can't be the worst option.
I crimped 2 wires here so I didn't need to have any more splices than necessary.

There is a hole in the bottom of the battery box under the wiring loom where we can run the wires out of the box.
Also conveniently there is a factory ground point between the battery and fuse box that you can use. I also put 2 ground wires here so I didn't need to splice again.

Now we just need to pick a way to route the wires to the fog lights. I ran mine with the harness into the driver side fender well by the washer bottle.
Route them to the drivers fog light, cut to length and attach your fog light connector that you robbed from the harnesses listed at the top or your aftermarket connector.
I ran the passenger side wires with the driver's side wires then along the lower radiator support and did the same, cut to length and attached the connector.
Make sure you give your self some extra wire so you can unplug the lights if you need to remove the bumper again.

Like when you decide you want to try to add the front view monitor camera. :cool: Or do it all at once like I did but I won't do a write up on that install since there is one on nasioc and the guy who did all the work figuring it out was trying to sell the harness you have to make. There is a thread on how to make the harness for that and where to order the connectors on reddit.

Back to our regularly scheduled content.

Now that we have all the parts installed, and wires ran, we can test our install.
Plug the fog lights in, clip the brown connector back on the fuse box, put the fuse holder back and make sure the rubber boot on the wire loom is seated properly, and install the battery.

Now we can light it up!

Turn the key on and turn the low beams on. Now push that shiny new button, your fog lights should come on.
They will only turn on with the low beams on. They will not turn on with the high beams or with the headlights off.
This is exactly like they would be if the car came with them from Subaru.

Again sorry for the lack of in-depth pictures but this was done a year ago.

I hope you all enjoy and forgive me if this went on too long, this is my first write up.
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This is great info, I'm getting ready to install fogs on my 2020 STI base and wonder if any new info has been discovered that I can test before I do. Or any success stories from this post? Thanks in advance!
Did you guys have a good idea of which wire to tap on the biu harness? I might be willing to try it just to add that info to this thread. This is the only good resource of info I could find on the topic. I ordered the OEM kit without reading enough and then realized it wasn't exactly what I wanted. I know that OLM sells a harness but if I read correctly it may not work with the 18+ STI, plus I really do not think I want to spend any more money on the project. Also I like the idea of this much cleaner install with less wires
Ok one more question before I do this also. The blue wire that you spliced into at the brown box, did you cut it from that box all together or just splice in, letting it still run where it did previously? Ite tough to tell in the picture.
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