How do you wire a light to signal thermo fans are on?

[pisso001]

Hi all,

Basically I want a small light to come on when my thermo fans come on so i know they are working how they should.. Ive done all the wiring of the thermo fans so it should be easy just wondering how to do it...

Thanks,

Chris.

[takai]

Just wire the LED into the switch power circuit.

[pauljones1976]

I would suggest using a Relay to run your light. Relays are cheap (less than $5 I think). Try Dick Smith Electronics or an automotive shop. Here is a diagram for how a relay works:



I'd cut your thermo fan power wire, one side of your cut to 85 & the other to 86 (ie wire the relay in series with the power wire), then wire a 12v LED between 30 and say the accessory fuse in your fusebox. Then run 87 to a ground (or the chassis).

This way, you do not affect the current (power) driving your thermo.

Cheers,
-Paul.

[takai]

Uh, you do know a relay is switched from post 30.
The LED will burn out if its used to ground a 10-20A thermo fan.
You have to run the light in line with the thermoswitch, not with the thermofan. Relay is assumed.

Also how you have suggested it the fans are on permanently when the accessories are powered.

[The Real Roadrunner]

Uh, you do know a relay is switched from post 30.
The LED will burn out if its used to ground a 10-20A thermo fan.
You have to run the light in line with the thermoswitch, not with the thermofan. Relay is assumed.

Also how you have suggested it the fans are on permanently when the accessories are powered.

Good points, the dude has the switch in there also though so it will be bale to be turned on or off as long as the ignition is on.

If you were putting in a switch that is not already in the car you can also buy switches that have lights in them which may make your installation easier.

Heres an updated pic but good pic to start with also


cheers
linden

[RA35GT]

Roadrunner, while your diagram will turn the light on, depending on the current draw of the light, pin85 on the relay may not be brought fully to ground (which would mean the relay wouldnt operate, thus disabling the fans).

Its much easier to just place a light in parralel with the coil in the relay. As per attached pic.

So everytime there is voltage applied across the relays coils the light will light up as well.

[The Real Roadrunner]

LEEROY was whoring not me,
he wanted to show off his famous paint skills or lack there of.

i would go with your setup if i was wiring but i dont do wiring as every time i touch a wire i get another grey hair.

cheers
linden

[pauljones1976]

Guys, please do not pay any attention to the diagram I had in my post - it was to demonstrate how a relay works NOT how to wire up the LED in question. It has been taken directly from another website and NOT MODIFIED. It shows how to wire up a relay for your lighting system etc.

There is no need for the switch as explained. Just that I did not remove it from the picture. I did not edit the picture so that it could be hosted directly from the original site.

Cheers,
-Paul.

[lexsmaz]

Hey Chris i would pressume you have relays already hooked up to the fans, so just peel back some of the insulation on the positive power wire going to the fan motor, & solder onto it a wire which you can then run back into the cabin, to a led light & just earth the other side of the light, this way you will know when the fans are actually working, not just the relay being tripped ( Make sure you have a good rubber grommet or such on the wire going through the firewall ) ... Led lights draw stuff all current ........ The whole things not really necesary but if it makes you feel better, Don't forget your temp gauge ..

[pauljones1976]

Lexsmaz, you are correct in saying that your way will actually indicate power flowing through the thermofan positive wire. However, it will still light the LED even if the circuit is broken at the thermo (ie: if the thermo motor dies) and that method will steal current from the thermofan(s) circuit. This is the reason I suggested putting a relay in series with the power wire to the thermo. That way you don't affect the thermofan circuit currrent (although the relay coil will draw a small amount more current) AND it tells you if the thermo is actually running. If it's not running, the circuit will not have current and the relay will not energize thus not engaging the LED.

Cheers,
-Paul.

[TA-022]

what lexs said is the best.

actually lights up when the fan is on.

all the other setups just say the thermo switch or relay works.

wanna know when the fans are on ... hook to the fan

[pisso001]

Thanks all for the suggestions.. I think ill use Lexmaz suggestion because its the simplest to set up.. Ill only be using the light for a little while until i get to trust the thermo fans are working how i want them to.. Thanks all, plus rep for all..

thanks,

chris.

[pisso001]

Also should i put a fuse in the line for the light? Its only a really small LED so probably good idea.. What fuse should i use?

thanks again,

Chris.

[hemi twofifteen turbo]

lol the LED should be a pretty good fuse. If everything was wired this way there'd be 1000's of fuses in every car. Just if your going to use an LED make sure you put a resistor in series with it otherwise you'll blow it.. say 580ohm.

[XR Pilot]

You don't need a fuse to protect the led, you need a fuse to protect the wire going to the led from shorting out. If the wire rubs through on the firewall, once your thermofans engage it will short out directly to ground. Just solder the smallest fuse possible inline as close to the thermofan as possible. If you do it neatly with heat shrink you won't even know the fuse there.

pauljones1976 - Yes, the led will 'steal' current from the thermofan circuit, but is in the order of 20-40ma, which is 0.04A, on a 20-30A circuit. If a led in parallel on the thermofan circuit causes problems, I would be taking a serious look at the thermofan wiring

[BradW]

Lexsmaz, you are correct in saying that your way will actually indicate power flowing through the thermofan positive wire. However, it will still light the LED even if the circuit is broken at the thermo (ie: if the thermo motor dies) and that method will steal current from the thermofan(s) circuit. This is the reason I suggested putting a relay in series with the power wire to the thermo. That way you don't affect the thermofan circuit currrent (although the relay coil will draw a small amount more current) AND it tells you if the thermo is actually running. If it's not running, the circuit will not have current and the relay will not energize thus not engaging the LED.

Cheers,
-Paul.

Putting the relay coil in series with the power wire to the thermo fans is not a very good idea. I don't think the relay coil will enjoy the thermo fans trying to pull 30A through it, it WILL burn out the relay coil . Also you add extra resistance and therefore voltage drop by wiring things in series.
Also a light hooked up in parallel with the thermo fans will not "steal current" from the fans. The pissy little amount of current the light draws will be supplied in excess of the current drawn by the fans (ie the whole circuit will draw the amount of current it needs to power the circuit).

I can't believe this thread has gone on so long for something that is so simple .