how to connect fan light ~ visible from inside of car

[j12piprius]

I connected a 12v led with resistor to the coolant fan relay. I scraped the edge of the relay socket and relay with an exacto knife, and drilled a hole in the top edge of the casing, to make room for the wire. The relay comes with 4 different numbers; 85 & 86 run a charge through the relay coil, 30 and 87 go to the device, in this case the fan.

Attaching the wire to #30 caused the light to come on immediately, showing that #30 was first inline and therefore the wrong one, because the light needs to be triggered by the temperature switch. I switched the wire to socket #87 and the light didn't go on, showing that #87 is correct, and only connects when stimulated to do so by the little coil in the relay.

Be sure to shove the relay to the bottom of the socket, to make sure it's connected. I routed this wire along the outside bottom edge of the frame with gorilla tape, with the light showing under the edge of the hood, outside of the window, and in a nice position to see from inside. I connected the other wire as a ground to the edge of the frame.

The light came with two 19.5 inch wires from luckybike on ebay for $2.95. Key words: Red LED Inline Resistor 12v Motorcycle Auto Diode Car.

Update:
The a/c fan caused the light to come on at 186 degrees. I removed a/c fuse #56, and the fan light came on at 206 at the peak of the hill. The light turned back off at 204, and went back down to 190. The led light and temperature range of the fan are perfect for me now.

[doviatt]

It's been years but if I remember right....I put a 12V led parallel to the fan after the relay. I found the two wires going to the fan and put a meter across them. When the car got to temp the fan kicked on showing 12V on my meter. Check one. Then ran wires from this location into the dash and hooked up the panel mount 12V LED (mind polarity). Check two.
Done.

Edit: on second thought this could have been a lamp (incandescent). No need for polarity check on this option. But won't look as cool as an led.

[j12piprius]

The light came on at 20 miles into my trip yesterday, at 186.8 degrees. I was surprised that the relay connected so soon, as I expected the temp to get closer to 200. The red led light works great, is bright and very easy to see.

The light stayed on from then on, most of the time at 186.8 degrees, to a peak of 194. I think the relay connecting in the 194 to 203 range would be better. I opened the bottom grill to half way for this trip.

[Daox]

I'm not sure your fan is actually is turning on. If you get a breeze through the engine bay, it will spin the fan and that permanent magnet motor will become a generator and light up your LED (its has happened to me). If you let it sit and idle until the fan is supposed to come on, it should turn on a good amount brighter than when you're driving.

[doviatt]

Good point Daox. I noticed with my incandescent fan light that it would run dim when the fan was windmilling and this varied with conditions. It would be full bright (unmistakeable) when the fan was actually on. Incandescent is more of an analog measure.

[j12piprius]

The light is connected to the relay, not the fan, and therefore is not affected by the wind.

[mcrews]

Originally Posted by Daox

I'm not sure your fan is actually is turning on. If you get a breeze through the engine bay, it will spin the fan and that permanent magnet motor will become a generator and light up your LED (its has happened to me). If you let it sit and idle until the fan is supposed to come on, it should turn on a good amount brighter than when you're driving.

another really SMART answer!!!!
Again, that's why I like this forum!!!!!

[Daox]

Originally Posted by johnlvs2run

The temp went to 205 when I stopped for directions, no wind, and the light was still at full brightness as before.

Also, I connected the light to the relay, not the fan.

So, you stopped and even though the fan was running the whole time your temp still went up higher? Something isn't right here.

[Cobb]

True Dat, cars do get warmer when parked then driven. Our old 82 vw rabbit would pop the electric fan on 5 minutes after parking and shut it off a few minutes later.

I noticed the ac in my scion xa wasnt as cold as it could be and the other toyota products had 2 cooling fans where as I had one. I added a second one to make it colder and it did so, lost 4mpg. I use to leave the fan on for short trips inside stores to aid in reducing under hood temps.

https://www.youtube.com/watch?v=rPcaGu70DS0

[gone-ot]

Put a diode in-line between the LED and the fan to "block" the DC-voltage that's being generated by the fan as it's windmilling and acting like a DC-generator.