Radiator Fan. by parkdrive

Could some one give me any advice.
I am thinking of fitting light(s) inside the car to idicate when the cooling fan come's on. Any one know if I can wire these into any conections under the bonnet.
My car is fitted (I think) with a 3 speed fan but I am mainly interested in the low speed, though fitting to all three would be nice.


Posted 20 Oct 2010, 20:34 #1 

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Yes it would be possible, but what are you after from the lights (s)?

They will tell you that the fan is supposed to have come on, but if the fan goes faulty (which is the usual failure) your light would still be on.

Or do you want the light there for some other reason?

If you are sure you want to do it, one of us should be able to advise.

The main thing will be to make sure you rate and fuse the wires correctly. I'll explain what I mean this evening (need to get on with work right now).

Posted 21 Oct 2010, 07:07 #2 

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As Duncan said it will only tell you that the fan should be running at said speed, but thinking a little further.

If the high speed light came on it would be more than likely there is a problem ( or very hot weather) as the low/ medium speeds on a three speeder usually take care of business.
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Posted 21 Oct 2010, 12:12 #3 

My Idea was that fitting a light for each fan speed, I could see when each speed was ( should be) running.
If for instance the low speed light came on and I looked at the fan to find it not revolving then I would know something was wrong.The same would apply to the other speeds.

Posted 21 Oct 2010, 15:45 #4 

I think the way to do this might seem counter intuitive, but this is the way I think it should be done.
The fan speeds are controlled by one or other relay switching the permanently powered motor to earth, the circuit in each case being through specific motor brushes. So, the fan doesn't receive switched power, it gets switched earthing. By the same token, your warning lights should be on a permanent (via ignition key) power supply. Their respective earth returns should then be the same as the corresponding fan circuits. In effect, you connect each bulb earth wire to the corresponding relay. You'd have to determine which connection on the relay provides the switched earth circuit. That can't be too difficult once you have access to the fan control box.


Posted 24 Oct 2010, 21:48 #5 

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I think TC is right, but I'm concerned what the ungrounded terminals on the fan might do. They are likely to sit at some intermediate voltage, and may ground the bulbs enough to cause a glow. May work fine, though.

If you do it this way, you would need to connect wire as thick as the fan wire, as far as a fuse for each circuit. After a low value fuse (1A) you could use 1A rated cable to the bulb. This is important because if you splice in thin wire, and it gets shorted, it would try to carry the entire fan current. The fuse would not protect the wire as it is designed to protect the big wire.

Putting an LED (Light Emitting Diode) on the drive to each relay might work better, and being low current means less risk in case of trapped wiring. I would think the diagnostics in the Engine ECU (Engine Control Unit) would live with the extra 20mA. Could probably connect in the plenum too, rather than at the fan end.

Posted 25 Oct 2010, 12:11 #6 

Thank you all for your advice/comments.
I did intend to use something like Neon type bulbs.but not being good on electric's I have no idea where to connect them in.
Perhaps someone could give me details or better still a sketch of how to do this.

Posted 27 Oct 2010, 10:02 #7 

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OK, first, Neons as such won't work. They need around 100volts so are fine on mains, but not cars.

LEDs would work. But to be honest, I'd be wary of doing things if you aren't reasonably experienced with electrics, as you might misunderstand something one of us says, and cause a problem on the car.

You need to check whether you have two or three speed fans, and tell us if it's petrol or diesel, as I don't think its the same on a diesel.

Posted 27 Oct 2010, 11:42 #8