Afternoon all

Just trying to tidy up all those annoying problems to which I have no answer.

I've fitted a fan overide switch to allow me to turn the fan on whenever I feel like it(seemed like a good idea at the time)

With the ignition on I flick the switch and hey presto fan is on and little light on dash lights up to tell me it's on.

Howver with the engine running it won't work so at the moment it's a bit pointless.

Here is how it's wired though it's a switched supply not a permenant. Any ideas what the problem is?

fan wiring

Have you checked the permanent supply is quite so permanent when the engine is running?

if you have wired exactly like that, then there should be bo problem.

check the fan switch - if it has 2 tabs, one of them may be connected to body thus to ground.

note that some relays have diode fitted so you should swap 86 and 87 round - I doun't think you have as you would have been blowing fuses.

Personally I like wiring up the fan truly permanently as it then the fan continuous to run after the engines switched off and helps cool the engine bay better rather than cook everything usually just after the engines been very hot and it just dumping all that heat in there.

As for why yours is not working I'm not sure, probably something simple

Mr Whippy it isn't permenant it's switched as in my post.

The fan over ride switch has three tabs, one from the relay, an earth for the light in the switch and the other goes to the dash light and then to earth.

So if it comes on with just the ignition on what could be preventing it from working with the engine running?

quote:

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Originally posted by jabbahutt

The fan over ride switch has three tabs, one from the relay, an earth for the light in the switch and the other goes to the dash light and then to earth.

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quote:

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Originally posted by jabbahutt
Mr Whippy it isn't permenant it's switched as in my post.

So if it comes on with just the ignition on what could be preventing it from working with the engine running?

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I'm assuming the rad fan circuit worked OK before the switch was added? If so then it's not an issue with the supply.

I'd keep it simple at the switch to start with. Don't bother with illumination, just find the two contacts that make/break when the switch is operated and connect them to the relay and earth. If that works OK, then start adding the spiffy bits.

Sorry for the omission of a bulb in the earth leg from the fan switch.

Surely that couldn't make a difference could it?

The fan kicks in automatically with the engine running using the rad switch

And with the engine off the fan works fine using the over ride switch.

It just doesn't work with the engine on.

I'll disconnect the switch tonight and try different options.

It could if the bulb is in series with the relay and earth (i.e. the path to earth from the relay goes relay-switch-bulb-earth). I'd provide the switch with a 12V supply for the illumination, and have the load and illumination sharing a common earth.

Try it without the illumination to start with.

Shirley the simple way to resolve this would be to get in there with a meter while the engine is running, and find out where the problem is (sounds like there's no supply with the engine running, which is what I think Mr W said)

John

Mr Whippy will testify that when it comes to electrics I'm not exactly what you'd call experienced.

I take it put the multimeter across each of the incoming feed pins one after the other and the other to a known earth and expect 12V?

quote:

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Originally posted by jabbahutt

I take it put the multimeter across each of the incoming feed pins one after the other and the other to a known earth and expect 12V( or thereabouts)?

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If it worked before the switch was put in it's not the supply...

Is the earth from the dash switch/lamp definitely wired to a hard earth?

You didn't tie it in to the same earth as the ignition lamp which obviously isn't really an earth but it would look like one with engine switched off.

Cheers
Davie

I had a similar problem when I wired an illuminated switch in parallel with the temperature switch on the radiator.
The switch would only energise the fan relay when the filament of the integral bulb was cold. If you turned the switch off and on again the relay would not energise - obviously something to do with the resistance of the filament and the common earth path?

here is circuit with simpl on/off switch as override.
Rescued attachment fan.JPG

and here is variant, as fitted to my land rover, with 3-position switch. The switch internals are not shown but it is standard lucas switch as fitted to series land rovers.

Note that I have 85/86 wrong way round but it doesn't matter as the relay does not have snubber diode.

either of thse circuits will do what you want to achieve.
Rescued attachment fan2.JPG

many thanks for the help. I've sat and looked at the way it's wired.

1. Firstly the dash bulb is wired onto into the earth leg of the over ride so it'l never light up if the fan kicks in due to temperature (DOH!)

2. So tonight I'm going to remove the overide switch from the circuit, rewire the dash bulb so it will come on from either switch.

3. Disconect the rad switch and short to earth and see if the fan comes on with the dash bulb.

4. replace the over ride switch and check that works both with the engine on and off.

5. If not working with the engine on rewire dash bulb earth to different earth source and start again.

fingers crossed all should then be well.

quote:

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Originally posted by jabbahutt
1. Firstly the dash bulb is wired onto into the earth leg of the over ride so it'l never light up if the fan kicks in due to temperature (DOH!)

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