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?

 

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.

 

Thanks Tree! I'll go test that now. 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.

 

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 ......

 

i would wire to a switched 12v source since you'll only need it when the car is running...

 

I used one of the Radio Shack 12v LED which already have the resister built in.

 

Thanks Will. It is wired to a switched source. Wouldn't want to chance the fan coming on while I'm working on the car.