Subaru BRZ Dome Light Controller

The dome light in the 2017 Subaru BRZ is rather old-school. While there is a body computer which controls the ON time and provides for a several-second dimming operation, it still has a manual OFF-DOOR-ON slider switch.

This is OK, and even kind of endearing (I kind of like how this car has "islands" of modernity that don't "talk" to each other as much as newer cars, though I suspect Subaru may have changed this in more recent years of this car); however ...

... the slider switch wears out quickly.

With this modification, the slider switch still functions normally, but now you can always turn the dome light ON by touching the switch body. You can toggle it OFF by touching it again. If you do as much "dashboard dining" as I do, this is a much better UI than man-handling this switch with its terrible mechanical action / feel.

Actually, this is a proximity switch: You need not actually touch it; with this design, getting your finger within about 2mm or closer for more than about 200ms will toggle it.

Further, the logic is not sophisticated: It is simply a logical-OR. If you have the door open and touch it, nothing will happen (it has no force-OFF authority).

But in all cases, sliding the switch to the OFF position will force the light off, and sliding the switch to the ON position will still force the light on.

First, replace the hot-burning festoon lamp with a 2700K LED version (e.g. from some aftermarket auto vendor); replace the lens (the same vendors offer some nicer replacements). If you don't do this, the plastic will probably yellow after a few years.

Note that you can see a lot of the components through the lens in my pictures. To the naked eye during normal use, you don't see this; the dome light looks OEM.

Fill the reverse-side "well" of slider switch with an electrode (e.g. braid or foil), connected to the center conductor of a shielded cable routed from your electronics board. Fill the "well" with epoxy.

See the schematic. The board is simply an Atmel AT42QT1012 proximity switch controller driving a relay. When the relay is activated, it switches the dome light ground-return "supply" away from the car (from the body controller, which provides a return path to ground) and instead to, well, ground.

This circuit takes continuous power but it is only a few mA so it does not matter.

Connect the BLACK-/RED+ (see schematic) wires to your electronics board from pins 1 and 2 from the OEM connector; this will supply a continuous GND and +12V.

In Subaru's design, there are no "wires", as such, coming from the OEM connector; they are more like steel "traces".

Then, cut the metal "wire" coming from OEM connector pin 3. This will go to the PURPLE (see schematic) wire to your electronics board. The "resumption" (other side of your cut) will come from the GREEN (see schematic) wire to (from) your electronics board.

Note that OEM pin 3 behaves like "switch closure to GROUND". (Actually, it comes from (goes to) the body computer for pulse-width-modulation (PWM) light dim control.)