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I hope someone out there can shine some light (no pun intended) on this for me. What i would like to do is hook up an LED light to come on when the cooling fans come on. I have a 1996 GL1500. With the engine cold, key in the run position, the plug right by the fans, I have power to both wires that go to the fans. But when the fans come on, i have no power to one of the wires.
Now here is what i did try I grounded out one wire for the LED, then the other wire i put into the plug (bench test) and the light is on only when the fans are off. How can hook it up so the LED light is on when the fans come on? Any help would be great. Thank you.
 

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Exactly. When you have no differential to the wires, ie: both measure 12V, the fan doesn't work. As soon as one of the wires goes to a ground potential, then you have a 12V powered motor.

Blue wire is 12V all the time, the black wire goes to ground when the temp sensor switch grounds.

Put the LED positive lead to 12V, and hook the negative lead to the wire that goes to ground when the fans kick on.

Just think backwards. Instead of giving voltage to kick on the fans, you are introducing a ground.
 

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The easiest way to wire up the light is to pair off the fan motor harness with a resistor for the LED making sure the polarity is correct.
 

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Blue Angel,

Silicone Sam and Ansimp are right on the money.

As you can see with my hand drawn thingy that there is always power going to the fan and until the fan gets turned on there will be power coming out of the fan too. When the sensor reaches its temperature limits and activates, it conducts to chassis ground via its own threads. That’s why you only see one wire going to this type of sensor.

The easiest way to hook up something is to take the power off the leads on the connector going TO the fan. This is what I did. I hooked up an amber LED pilot light to my circuit. Mine was not polarity sensitive. Some are and will be marked which lead is +. LED pilot lights are much easier to use and see than going with a discreet resistor and small LED. No fuss no muss.

I like the LED pilot light and it works well.

Tim.
 

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