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Picture of Subaru BRZ Footwell Light Controller

I purchased a 2017 Subaru BRZ ...

The Subaru BRZ is a fun and affordable sports car that seems to have a pretty big aftermarket following. Every day it puts a smile on my face, and no, Subaru is not paying me. While underpowered, it hugs the road like superglue and steers with the resolution of an electron microscope. It comfortably earned its keep amongst a bunch of Dodge Vipers at a recent car rally I attended.

I wanted the under-dash footwell illumination option ...

There aren't a lot of options -- these cars are pretty "loaded" with features, especially if you purchase the "Limited" trim. One of them is lighting under the steering wheel and glove box at night -- a blue or red glow.

But it was not available, and for good reason ...

Few if any dealers offer that option. My guess is that there's a good reason for this -- the illumination is always on at 100% intensity whenever the headlights are on. Instead of providing a pleasant and classy touch, this quickly becomes annoying.

So I installed the OEM kit, but with a twist ...

I solved the problem by purchasing the OEM kit myself (turns out it is a dealer-installable option, apparently meaning that it's not installed at the factory) and adding a simple controller box.

About the OEM kit ...

The OEM kit part number from Subaru for the BRZ is H701SCA100 (blue); it's also available in red. The cost is about $130, and includes a wire harness, two LED modules, and some minor hardware. It does not come with instructions; you'll have to download that from the Subaru web site at (Subaru Technical Information System). You do not need a subscription to download the PDF.

An alternate (simpler) solution ...

I have heard of other people solving the always-on problem by simply connecting the LEDs to the dome light. That way, they'll follow whatever the dome light does, including a 2-sec dim sequence, coming on when the doors are opened, etc -- pretty much what you want. The other advantage is that it's MUCH EASIER to install that way, because it turns out it's easy to route the wires across the top window edge and then down the A-pillar on the passenger (or both!) side(s). By the time I found out, I was already well into this project, and anyway, I wanted to do something a little bit more customized.

So I made a Delay & Dim controller ...

When the car headlights go from off to on, the controller keeps the floor lights on at 100% for 2 minutes, then takes about 2-3 seconds to dim them to about 10%, and they then stay that way "forever" until the car headlights go off. Whenever the headlights are off, the floor lights are off. The 2-minute delay, the dim rate, and the 10%-dimmed-level can be set as desired before installation but can't be adjusted afterward.

The controller is analog ...

This is a simple 555 timer-based circuit straight from 1975. True, nowadays few would take such a low-tech approach. One would use a microcontroller; I like the Atmel ATtiny10 or ATtiny102 for this kind of application. But I felt like doing this one project all-analog because this way:

  • There is no chance of RF interference with the radio, which is very close by.
  • No chance of PWM strobing / flicker. This drives me nuts, especially anywhere in an automotive environment. No doubt that would be the way I'd have to control the dimming, and these lights are in your peripheral field of vision, where your eyes have very fast response time. (The D/A output on most micros would probably be the way to go.)
  • I'd have to add extra parts to a micro / Basic Stamp / Arduino anyway, to be sure that there wouldn't be a problem with chips wanting less than 12V Vcc and conditioning RESET in the abusive power on-off-on start/ramp environment of a car.

So hold your flames :-) -- If I were making this as a sellable product, of course I would use a microcontroller!

Step 1: Overall Tips for Installation

  • Budget an entire day for this if you are relying on daylight.
  • It will take 2 people to remove and replace the radio because it's heavy, awkward, has 6-8 connectors, and has a front touch screen that you don't want to damage.
  • The hardest part is disconnecting (and reconnecting -- be sure it clicks!) the connector that plugs into the back of the clock/hazard panel; this has to be done backwards in a mirror. All Subaru connectors have a tab to push in to release them (in the clock/hazard case, the tab is facing down), and Subaru loves to make them require about 30 pounds of force.
  • Tether your tools so you don't drop them down the hole.
  • Follow the instructions -- Disconnect the battery! Do not skip this step. I've heard of people blowing up the body computer, etc. Now, it's possible those are just unlucky ones who short things to ground with metal tools, but why risk it. And who knows what trickle power is going in/out of that radio, which goes to body stuff, the camera, the microphone, active antennas, etc. Just disconnect the battery. About the only thing you'll have tor reset is the clock and one or two cluster indicator prefs. All radio settings are kept. When reconnecting the battery, be very careful you tighten it enough! Try gently to rotate it on its post using its ground bracket as a lever arm -- it should not move.

Great work! Want to add foot-well lighting, but don't want to spend $130; I like your customization, but that's way over my head. Do you recall which pins the yellow (pwr) & black (gnd) connect to on the hazard/clock unit?

BenKoning (author)  acuratlsfan1 year ago

I don't, unfortunately. But it is very obvious if you get the harness from the kit (which of course doesn't help you as you're not getting it). And the problem is that you can't test it easily, either (e.g. by using a voltmeter and testing the pins), with the battery disconnected. Also, without the kit-supplied harness with its two connectors, how are you gonna tap into the car to get the +12V when the lights are on? Another way would be to probe the various wires in there, but that's hit-and-miss plus you're gonna be somewhat damaging the wires by sticking needles in wires. Really: Just spend $130, it's not worth the headache otherwise, LOL.

Or, why don't you just do this: Buy two red/blue/white/whatever LEDs from wherever, add a series resistor inline for each LED (resistor like 1K-ohm to 10K-ohm to your liking; remember that you need to drop 12V down to much less than 2V else you'll blow up the LED and possibly blow a fuse or even damage something in the car). Also careful about LEDs is that polarity matters. (I could tell you how to hedge your bet against this with a rectifier bridge, but it looks like you want to stay away from too much electronics.)

Then wire both LEDs to your dome light. (CAREFUL: if car battery is connected, do NOT work in the dome light receptacle with metal tools. If you short the the dome light (easy to do), you get to have your dealer install a new body computer for $600-ish. Just disconnect your battery.)

I *think* it's easy to route your wires down the A-pillar on the passenger side. You could then daisy-chain to the driver's side, probably without pulling out the radio or anything.

That way:

You don't have to disassemble anything in your dash

You arguably get a better operational result than even me

You have full choice of what kind of LED

The only con is that you'll have to make a little bracket or something to hold your LEDs pointed straight down. I'm imagining a piece of plexiglass with some holes.

DaveLyons1 year ago

Nice! The thoroughness and detail is something I'd like to see in many other Instructables.

Great first Instructable. You should enter this into the First Time Authors contest.