[the82elco]

ok i have dual electric fans & i wanted to know is there a way that i can hook up a LED light inside my car so when the fans come on the LED light comes on

[dogwater]

Use a relay,SPST common 4 pin.

[the82elco]

Originally Posted by dogwater

Use a relay,SPST common 4 pin.

so ill just have to run the led hot wire to the relay and ground the other wire?

[EOD Guy]

You can run a wire from the fan side of the fan relay back to your light..... ground the other side of the light and when the fan fires up so will the light.

[toddalin]

If you want to use an LED, just wire it in parallel with the fan motor and use a 1/4 watt, ~1,000 ohm resistor in series with the LED. Any value between ~500 ohms and 1,000 ohms will work fine. A lower value will result in a brighter LED, but possibly shorter lived. Alternatively, you can buy LEDs for 12 volts, and they typically include a 470 - 1,000 ohm resistor in series.

The LED is polarity sensitive and the longer lead goes on the + terminal. But if you hook it up backwards it won't do any harm. It just won't come on.

[vicrod]

The LED should be connected in parallel with the coil of the relay. The circuit that is typically used is as follows.
The coil has a ignition switched and fused source on one of the terminals.
The other terminal of the coil gets connected to the temperature sensor which closes when it reaches it's rated temp. and completes the circuit to ground.
Connecting the LED to the coil is preferred for (3) reasons.
The wire only needs to small (#18) as the load of the coil is very small.
And when the LED is connected to the fan side of the relay the wire will need to be the same as the wire going to the fans or at least fused if the wire is smaller.
And the fans will feedback voltage to the LED as they coast to a stop and sometimes will continue to turn when the car is moving.

vicrod

[toddalin]

Originally Posted by vicrod

Connecting the LED to the coil is preferred for (3) reasons.
The wire only needs to small (#18) as the load of the coil is very small.
And when the LED is connected to the fan side of the relay the wire will need to be the same as the wire going to the fans or at least fused if the wire is smaller.
And the fans will feedback voltage to the LED as they coast to a stop and sometimes will continue to turn when the car is moving.

vicrod

Not if connected directly across the fan motor leads that actually go right to the fan motor.

The wire can be as small as you choose because it only carries about 14 (@ 1,000 ohm) to 28 milliamps (@ 500 ohm) for the LED,

i.e., (13.6 volts - ~1.6 volts for the LED)^2/1,000 ohms = 14 milliamps

No fuse is necessary for just an LED.

The LED is direcly across the fan motor. When the motor stops receiving current, both the fan and LED go out. There is no way that the fan can continue to spin under it's own current produced by the rotation of the motor, though the LED may remain on for a moment after shutdown as the fan winds down.

[dogwater]

Just a quick quistion,would an LED act like a diode,because it is in a sense it a one way.

[EOD Guy]

LED stands for Light Emitting Diode......... It won't take very much current tho

[Frankinforesthill]

Yes it will act like a diode.
It is a diode.

[vicrod]

The load of an LED is insignificant and not an issue when wire size is concerned. The capacity of the circuit and the protection of that circuit is the factor by which a wire size is selected.
For example a cooling fan could have a 30 amp or larger fuse and #12 or larger wire. Connecting a #18 wire to that circuit is not a good idea when you consider that that #18 wire can become shorted. #18 wire does handle 30 amps well. A very hot wire will result.
That is the point I was trying to make.

vicrod

[the82elco]

ok i got a 12v led light to run to my fans so i no when they come on. i wired the light up to the power wire on my fan & grounded the other inside the car when i did that the led was lit up with the car off / how do i get it to come on only when the fans com on??
im also have a override switch

> this is the led
> the fan controller

[Joe G]

Originally Posted by the82elco

ok i got a 12v led light to run to my fans so i no when they come on. i wired the light up to the power wire on my fan & grounded the other inside the car when i did that the led was lit up with the car off / how do i get it to come on only when the fans com on??
im also have a override switch

The fan controller you have pictured is a Derale 16759. They control the fan by switching the ground on and off rather than by switching the power. So you will need to change the way you have your LED wired. Based on the Derale wiring diagram, I would suggest connecting the LED's positive wire to the controller's yellow, and the LED's negative to the controller's red wire.

Hope this helps....

Joe G.