switch off led when engine starts

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=102379
Printed Date: July 12, 2025 at 12:54 PM

Topic: switch off led when engine starts

Posted By: spaspecker
Subject: switch off led when engine starts
Date Posted: February 20, 2008 at 4:43 PM

hi guys -

tried to cover this before, followed instructions here but that's not what I'm looking for, as the LED is lit all the time when the engine isn't running.

What I want is this: I have a pushbutton ignition setup in my car. I have got a new button that has a LED built in. I want to be able to put my key in the ignition, turn the key to switch on all the electrics etc. and have the LED light up. Then, when I push my start button and the engine starts, I want the LED to go out and stay out, until the next time I start my car.

Can anyone help?

thanks in advance

Replies:

Posted By: KPierson
Date Posted: February 20, 2008 at 4:58 PM

Without using a programmable microcontroller thats going to be a pretty difficult task.

How about this:

wire the LED + to igniton through a relay (LED + to pin 87A, IGN to pin 30).
wire the LED - to ground

Wire the coil (Pin 85) of the relay through a diode to the starter wire. After the diode (between the diode and pin 85) make a connection to pin 87 of the relay.

Wire the other side of the coil (pin 86) to ground.

When you turn the ignition on the LED will get powered through the NC contact of the relay. When you crank the car the starter will energize the relay. Once the relay is energized, the ignition power will cause the relay to latch in, which will turn the LED off. The relay will stay latched until the ignition is turned off.

-------------
Kevin Pierson

Posted By: spaspecker
Date Posted: February 20, 2008 at 5:12 PM

blimey - that was quick!!

I'll give it a go and let you know, just to clarify when you say pin85 through a diode to the starter wire, do you mean 12v switched, or key side or starter motor side? I've already wired up the push button ignition like here so I need to make sure I get it right.

Posted By: spaspecker
Date Posted: February 20, 2008 at 5:14 PM

also forgot to ask, pin85 diode - which side is the diode stripe facing?!?

Posted By: KPierson
Date Posted: February 20, 2008 at 6:05 PM

It would go to pin 87 of your push button start relay - starter motor.

The strip of the diode would be on the relay side.

-------------
Kevin Pierson

Posted By: spaspecker
Date Posted: February 20, 2008 at 6:08 PM

many thanks, BTW - did you ever get that start/stop kit for the altima/350z sorted out? I would be VERY interested if they became available