I had the unfortunate experience of leaving my car parked in D gear with the emergency brake (aka hand brake) off. It rolled downhill and sustained some damage. Seems like the mechanism to stop me from getting the key out unless I'm in "Park" is broken.

I'd like to set my car (a 2006 Mazda 3) up with some sort of a warning system. Something similar to having a buzzer sound if the emergency brake is off and the driver door is open.

I've not been able to find such kits online to be purchased. Am I using the wrong search terms? Might anyone be able to point me in the right direction? Instructions for a DIY project would also be most welcome.

  • That's weird. On most automatics, you can't even take the key out unless the car is in park. – 3Dave Aug 27 '18 at 17:26
  • @3Dave I've edited my question to reflect that the safety mechanism that locks the key when not in Parking gear is broken in my car. – urig Sep 4 '18 at 16:24

You're looking for two switches/circuits.

  • The "door is open" circuit, which closes/energizes when a front door is open. The main purpose of this circuit is to light the dome light.

  • The "Park/neutral safety switch" which (hopefully) opens when the car is in park or neutral. This is normally an interlock with the starter motor to keep you from cranking the engine in drive. You may get lucky and also find a "Park safety switch".

If you're very lucky, the park/neutral switch operates by grounding out its single wire. Also look for extra unused contacts on the park/neutral switch. The goal is to find a switch which grounds out *when the car is NOT in park.

You are more likely to find a "ground if parking brake on" switch on the parking brake. Check its action: if it has unused contacts, you may find it has a "ground if parking brake off" mode.

If all else fails, get a limit switch and mount it appropriately. It will also work to use a magnetic reed switch and glue a neo magnet to the correct location so the reed switch opens in Park.

This makes it a simple matter of a diode and a buzzer of choice. The diode is to prevent unwanted backfeeding.

When you open the door, the "open door" circuit is energized. Current flows from this source, through your diode, through your buzzer, through the not-in-park switch if closed, to ground.

| improve this answer | |
  • Thanks. I have my weekend project cut out for me. Any idea where I find can guidance on the right entry points into the electrical system? Wiring close to the break handle looks rather complex: img.photobucket.com/albums/v213/manofthefield/2007%20Mazda3/… – urig Jun 14 '17 at 10:23
  • 1
    You have to either follow the wires, or get a service manual for the vehicle that shows wiring diagrams. Honestly I don't even know where to go for post-2000 vehicle manuals, they are so computerized the book would have to be a foot thick or on CD-ROM. – Harper - Reinstate Monica Jun 20 '17 at 16:22
  • Thanks. Found the wire for the emergency break. It's green and white and attached to a microswitch at the base of the handle. Now trying to searching for the switch that triggers the light when the door is open :) – urig Jun 20 '17 at 19:18

Well, the thing is, you already have this two different ways in the car.

  1. If the transmission is not in Park or Neutral, the ignition should not release the key.
  2. If you open the door and the key is still in the ignition, there's a beep or a buzzer that will let you know.
  3. The hand brake, when applied, turns on a red light on your instrument panel.

How did you get the key out of the ignition with the transmission in D?

| improve this answer | |
  • My car is a 2006 Mazda 3. Features 1 and 2 are not implemented in this model. – urig Jun 12 '17 at 6:38
  • @urig Yes it is --> repairpal.com/… and mazda3forums.com/95-maintenance-care/… – tlhIngan Jun 12 '17 at 6:43
  • Thanks but that's not the case in my car. I live in Israel. Maybe in the US the car did come with these enabled? Would love to enable these myself but don't know how, hence my question. – urig Jun 12 '17 at 7:19
  • 1
    @ tlhingan I stand corrected. Heard from mechanic today that the fact that the key can be released when the transmission is not in P/N is actually a malfunction in my car. Going to fix ASAP. Tx!I stand corrected. Heard from mechanic today that the fact that the key can be released when the transmission is not in P/N is actually a malfunction in my car. Going to fix ASAP. Tx! – urig Jun 24 '17 at 18:39
  • 1
    @urig I was surprised to hear that this wasn't a standard safety feature everywhere in the world with large manufacturers like Mazda. Cars rolling down a hill on their own, like what happened to you, is easily avoided by this safety feature. Glad you found out about it! – tlhIngan Jun 25 '17 at 0:30

Why not use a small 12v buzzer, relay and a push type switch (push to close) fitted to the handbrake so that if the door is open the buzzer sounds : just have the relay "earth" through the door switch - may need a diode though (otherwise the relay could earth through the interior light). Another solution fit a second door switch...

| improve this answer | |
  • The headlight buzzer does have a diode in it already. That is why it buzzes when there is voltage at the lights, and ground at the ignition, but not when there is voltage at the ignition and ground at the lights. – rpmerf Jun 12 '17 at 15:34

I'm working on an electronic alarm that will sound if the parking brake is left on when the vehicle is put in gear. It will also sound if the vehicle is taken out of gear (put in park or neutral) with the parking brake off. I've built a prototype of this all electronic alarm kit and successfully installed it on my motorhome. I hope to put it on eBay soon as a marketing test. It should cover your needs nicely, and then some.

| improve this answer | |
  • Welcome to Motor Vehicle Maintenance & Repair! – Cullub Aug 28 '18 at 3:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.