Idiot light
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=5519
Printed Date: June 27, 2025 at 4:27 PM
Topic: Idiot light
Posted By: alansmith54
Subject: Idiot light
Date Posted: November 16, 2002 at 1:32 PM
Here is one for anyone who can answer it. I want to install an idiot light in my car. I want to wire up a relay so that when the car is off the relay puts out a 12v pulsed output to flash an LED. When the car is on the 12v pulsed output should be off. If anyone knows how to wire up a standard 30amp relay to do that please let me know, email me at alansmith54@hotmail.com Thanks in advance
Replies:
Posted By: melvyn
Date Posted: November 16, 2002 at 5:34 PM
Take an ignition +12 feed to the 85 terminal on your relay, and connect the 86 terminal to ground. Connect a constant +12v to the 87a terminal, and connect the 30 terminal through a 470 ohm resistor to the anode side of a flashing LED (such as Radio Shack item 276-308), and connect the cathode side to ground.
Posted By: go2pac
Date Posted: November 17, 2002 at 12:46 AM
No need for a relay. Wire up a flashing led direct with the correct limiting resistor.
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Karl
Pacific Accessory Corporation
Mobile Audio Interfacing Equipment
Connecting You to Your Music Since 1976
Posted By: PLAYER69
Date Posted: November 18, 2002 at 5:20 PM
Buy a flashing LED (preferably 12v already) and hook the longer lead up to 12v + live and the shorter lead up to the vehicles accessory wire that is live when key is on and ground when key is off. This way the led will flash when the key is off only.
Posted By: alansmith54
Date Posted: December 12, 2002 at 8:10 PM
What happens when the ignition is in the off position, will the flashing LED allow current to flow throught and thus loop the power through the LED and burn the LED or some wiring??
Posted By: webguy
Date Posted: December 15, 2002 at 3:38 PM
Nope, the current flow thru an LED is only about 11 ma. That much current won't even lite up a flashlight.
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Clean tools = Clean work!
Posted By: alansmith54
Date Posted: December 24, 2002 at 12:06 PM
New problem, just wondering if any knows an answer. After installing the idiot light and getting it to come on and off when I want, I have encountered something new. I purchased a flashing led which is great but the bloody thing flashes to fast making it appear to be on all the time and just get brighter and dimmer. Just wondering if any knows why this is happening and how to fix it. Thanks in advance for anyone with an answer.
Posted By: carguy411
Date Posted: December 24, 2002 at 12:16 PM
um heres a thought y not just buy a varard hyper led. no worring about anything just hook it up with three wires and there alot brighter thatn the readio shack leds
Posted By: alansmith54
Date Posted: December 26, 2002 at 1:21 PM
That sounds easy but, I already bought 6 flashing leds and I want to use them so if anyone knows if there is a resistor or something to put inline with the led to slow down the flash your help would be greatly appreciated. Thanks in advance again
Posted By: tekky
Date Posted: January 12, 2003 at 4:07 AM
I could be wrong (been 2 years since I've really applied electronics... but a capacitor would slow the flashing down ;) as in order to light up the capacitor would need to be charging if I recall rightly and as it discharges the led would go off... then you just play with the value of the capacitor to change the delay... Hope that helps... and maybe someone can suggest a Farad rating for the cap for a decent rate of flashing... I forget the formula for decided that :( ------------- -Karl Tiedt
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