Adding an LED to a relay?
07-31-2012, 07:08 AM
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Car: 1988 GTA
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Adding an LED to a relay?
I got a variable coolant temp switch for my secondary fan. It comes with a relay. The relay works differently than I am used to. Instead of activating the positive leg of the fan, it activates through the negative leg. So the fan positive is wired directly to the battery. The fan negative goes to the red input wire on the relay. Coming out of the relay is a black wire to ground. I want to add an LED in the cockpit so I can tell when the fan has been activated. Would I wire the positive side of the LED to the negative black wire coming out of the relay and the other side to ground?
07-31-2012, 07:33 AM
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Car: '86 TA
Engine: '74 350
Transmission: 700r4
Axle/Gears: 2.77
Re: Adding an LED to a relay?
No. Wire the pos side of the LED (anode) to 12V, and the neg side (cathode) to the fan negative. Ie, paralleled across the fan. Don't forget a current limit resistor.
Note- if it's just a relay output, you should be able to put it (relay contacts) in either the pos or neg fan wire as you wish, it's just a set of contacts.
Note- if it's just a relay output, you should be able to put it (relay contacts) in either the pos or neg fan wire as you wish, it's just a set of contacts.
Last edited by TreeFiddy; 07-31-2012 at 07:35 AM. Reason: Couldn't get brain together on last line
07-31-2012, 08:48 AM
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Re: Adding an LED to a relay?
No. Wire the pos side of the LED (anode) to 12V, and the neg side (cathode) to the fan negative. Ie, paralleled across the fan. Don't forget a current limit resistor.
Note- if it's just a relay output, you should be able to put it (relay contacts) in either the pos or neg fan wire as you wish, it's just a set of contacts.
Note- if it's just a relay output, you should be able to put it (relay contacts) in either the pos or neg fan wire as you wish, it's just a set of contacts.
It also has an override connection you can either wire to the AC positive or a switched 12v source. That is why I was afraid to alter the instructions. I'm used to everything working off ground.Thanks again.
07-31-2012, 06:07 PM
#4
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Re: Adding an LED to a relay?
your battery should be between 12 and 14v, most red leds are rated around 2.2v at 20ma... so you would need a resistor value of about 500-600 ohms rated at 1/2w ......
07-31-2012, 06:38 PM
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Re: Adding an LED to a relay?
i would wire to a switched 12v source since you'll only need it when the car is running...
07-31-2012, 08:45 PM
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Re: Adding an LED to a relay?
07-31-2012, 08:46 PM
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