Miata Ignition Switch Light
Page 1

This is the LED ignition light I made in order to better see the ignition switch in my 1994 Miata at night. The light is designed to to provide just enough light to see the ignition switch at night. It's activated by opening either door and stays lit for approximately 10 seconds after the doors are closed. It sticks out of a hole I drilled in the center dash, directly across from the ignition switch.
It works really, really well. In fact it works so well and looks so cool that I'm half tempted to rewire it to stay on as long as the engine is running and maybe wire up a few more lights to highlight other unlit controls at night like the power window switches, door handles, fog light switch, etc...

I used an LED light for three reasons. 1) An LED draws less current, making it easier to make t fade out after the doors are closed. 2) Some modern LEDs are hella bright. 3) They have this handy flange at the base so all you need is a hole to stick it in and you're done.
You could theoretically use a regular flashlight bulb or interior lamp, but keeping it lit after you close the door will be harder since it draws so much more power. Realistically, you would want to use a real delay circuit, not just a capacitor like I did for the LED. If you already have one of those cool interior light dimmer things, then just use that.

Here is a diagram of the circuit. When power is applied, it instantly charges up the capacitor and lights the LED. When the power is removed (you close the door) the LED continues to be powered by the charge in the capacitor for a number of seconds. The bigger the uf rating of the cap, the longer your light will stay lit.

I connected mine to the passenger footwell light as a power source. In order to do this I also had to connect a diode. This keeps my circuit from trying to power the footwell light when you close the door (which it wouldn't do very well). I didn't note this in the circuit diagram since you are free to connect yours to what ever source you like.

The important things are as follows:
  1. The LED. I used a green one. It matches the dash lights and just happened to be the brightest LED I had on hand. If I were to buy one, I would have gotten white (expensive) or amber. For those who don't already know, LEDs only light when current is applied in the right direction. They also burn right out if you use too much current, much less current than a incandecent bulb would, which brings us to...
  2. The resistor. This must be in place in order to keep the LED from burning out. I used something around 150 ohms. If you apply current to an LED without a resistor in place it will be runined in the flash of an eye. By using Ohm's Law (look it up yourself) you can determine how much current will go through your LED based on the resistor. Make sure you aim for something within the LED's rating (if you know it).
  3. The capacitor. The higher the capacitance, the longer your light will stay on after you close the doors. I used a 2000uf, 16V cap. (Okay, I lied. I really used one 1200uf and one 600uf cap, wired in parallel to provide 2000uf. But it does the same thing.) Most bigger caps are polarized, meaning that you have to hook them up specific to the polarity of the circuit. They will either not work or will die if you connect them backwards. If your cap is polarized you will be able to see the negative side printed on the body, like this:

    Each of these capacitors is showing you it's negative side, based on the stripe and/or series of negative signs (-).
  4. The door switch. So that you can use the interior lights without the door open, the door actually provides a switched NEGATIVE source, not positive like you would expect for most other circuits. This is important since both your capacitors and your LED need to be connected the right way in order to work.

Next page to see pictures of the light going in the center console.

Copyleft Mark Leinhos
Last modified 08/04/15

Smir nir bor de boor skih dish skih door
smir nir dir boor nir dir mmm
bork bork bork!