I am trying to get a switch to work for my rear fog light so that the LED light on the switch lights when I switch the fog light on, only trouble is that it is switching through a relay and is a switched earth.

Currently if I have my lights off and throw the switch, the LED lights but the the rear fog doesn't. When the lights are switched on and the switch is on the LED doesnt light but the Fog light does come on and so does the warning light on the dash.

The switch I have is like this,


Description


and the switch is wired like this


Description

If I disconnect the earth from the LED it obviously doesn't light but I would prefer it to but would this then be a problem at IVA if the light on the switch didnt light even though the warning light does?

since tell-tail cannot be 'confusing' no it probably wouldn't pass iva
I suspect the switch lighting is led, and as such only works in one polarity,
so: try swapping the connections on the back of the switch.

edit, looking at your switch diagram, its never going to work, unless you can reverse the led, and take it to 12v

[Edited on 16/11/16 by gremlin1234]

Do you have a circuit diagram of how the lights / fog light are connected?

Cheers
Davie

Sorry not really, It is using a Premier wiring loom and the sierra stalks etc. All the guide says is that it is using switched earth and that it is switch through a relay. With the lights off the fog light will not swicth on, once the lights are switched on I can then switch the fog light on too, if that helps.

If I was to use another relay that operated when using the switch I could use the relay to make the circuit and have a positive supply to the LED?
it would mean using another relay I suppose, would that work?

[Edited on 16/11/16 by tims31]

I also use a Premier loom, and followed some instructions found on LCB to sort the rear fog. (A brownie point to whoever it was!)

Yes, you will need a relay, wired thus...

+12v switched feed to pins 30 AND 86

Break into the brown/black wire that runs over the steering column to connect the left & right stalks, & run a feed from there to pin 85

Pin 87 goes to the fog switch

That's it.

Is it possible to take the switch apart, turn the LED around and the give it a 12v feed to the external wire?

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Originally posted by turnipfarmer
I also use a Premier loom, and followed some instructions found on LCB to sort the rear fog. (A brownie point to whoever it was!)

Yes, you will need a relay, wired thus...

+12v switched feed to pins 30 AND 86

Break into the brown/black wire that runs over the steering column to connect the left & right stalks, & run a feed from there to pin 85

Pin 87 goes to the fog switch

That's it.

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Here's how it works (I hope!)

Power comes into relay pin 30
Pins 85 & 86 are a switch - 86 is the switch positive, and 85 the negative
Wired as it is, there is always power to pin 86, just as there is to pin 30
But pin 85 doesn't get earthed until the headlights are lit by operating the stalk
When that happens, the switch is made, allowing power to reach relay pin 87 & from there to the fog switch

So it's the relay that looks after the earth switching - not the fog switch

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Originally posted by turnipfarmer
Here's how it works (I hope!)

Power comes into relay pin 30
Pins 85 & 86 are a switch - 86 is the switch positive, and 85 the negative
Wired as it is, there is always power to pin 86, just as there is to pin 30
But pin 85 doesn't get earthed until the headlights are lit by operating the stalk
When that happens, the switch is made, allowing power to reach relay pin 87 & from there to the fog switch

So it's the relay that looks after the earth switching - not the fog switch

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No. If switch is swithed earth, then how can the led light up.

Lets start at beginning. How many pins has the switch. When switch is on, which pins are connected together. What is each pin connected to,

Like i said rotate LED and add ignition live

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Originally posted by 02GF74
No. If switch is swithed earth, then how can the led light up.

Lets start at beginning. How many pins has the switch. When switch is on, which pins are connected together. What is each pin connected to,

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That's wrong that diagram I'm afraid.

You should have a Load, supply, and an earth to the switch. The led will take its power from the supply and once the switch is thrown it will be grounded via its earth and light up.

I've drawn this quick to show how I would wire it up.

The sidelight switch can either be before or after the relay but it is usually best to switch the earth.

Once the sidelight switch is 'on' power will energise the relay and light the sidelights.

This will also provide 12v to the fog switch, so when that is switched, its internal LED will light, it will energise the fog relay and 12v will flow through the fog light.

This means the fog light cannot light without side lights on.

the +12v supplies in my drawing should be fused supplies.

Easy......give the led a live supply (ignition) and wire the "earth" to the live side of the switch.....the led will only come on when the switch is in the "on" position.

Note: the live supply for the led at the switch can come from any convenient supply nearby......

[Edited on 17/11/16 by snowy2]

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Originally posted by snowy2
Easy......give the led a live supply (ignition) and wire the "earth" to the live side of the switch.....the led will only come on when the switch is in the "on" position.

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I'm only an amateur, & all I can say is that my rear fog is wired exactly as per Tims31 diagram. It works fine & passed IVA.

The only caveat to that, is that my relay pin 85 tees into the headlamp switched earth wire that runs across the steering column. I'm not sure exactly what's going on with that in his diagram.

I don't see how you can rotate the LED pins. Being a diode, it only allows the current to flow in one direction (if I remember my physics correctly).

I'm wondering if perhaps the problem here is terminology.

My rear fog switch is just an ordinary 3-pin job that allows current to reach the whatever-it-is when it's in the 'on' position. I've never come across a switched earth switch. Is there such a thing? I suspect Tims31's switch is the same as mine.

If so, then as ste says there should be a pin for each of load, supply and earth. On mine, supply is marked as +12v (from relay pin 87), load is marked A (Appliance, ie the foglight + pin) with earth being the usual earth symbol (from any old earth).

Tims31 says that pin 3 on his switch is:

"LED -linked to supply pin"

I would expect that to be the LED earth, as per his diagram.

then that:

"Loom has two wire that complete the circuit which is the switched earth connected to pin one and two pin three goes to earth"

I make that 3 earths - again not as per his diagram.

Remember, too that the fog wiring in the PWS loom predates the current IVA regulations, so it will need modifying.

ste's diagram is too advanced for me, but he does mention sidelights. I would just remind folks of what IVA says, which is that rear fog switch must not operate with sidelights alone. It has to work only when the headlights are on, and must go off when the headlights are off, even if the switch itself is in the 'on' position.

HTH

Hi turnipfarmer

Your probably right that my terminology is wrong and for that I can only apologise.

The PWS loom is wired so that the fog lamp will only light when the main/dip beam is on and the fog light goes out when these are switched off (The fog light does not light on side lights). Alan states that for the Sierra stalks using this loom it is a Switched earth which is why I mentioned it but that seems to be confusing the matter.

From the loom I have one wire that goes to my dashboard with the Warning lamp and this is earthed and illuminates when the fog light is switched on

I also have another two wires (Brown/black) that are for the switch. One comes from the sierra stalks which seems to be the load side and I assume the other comes from the Relay that switches and is the supply.


Description

If I wire the switch up using pin1 (supply) from the relay, and pin 2 (Load) the switch operates as expected just that the LED does not light and it won't as Pin 3 is not connected to earth

If I connect Pin3 to earth then it still works the same just that the LED only lights if the Main lights are off and the switch is selected to ON

Sorry but I have got confused over the term switched earth

If I was to use a relay to switch the earth and the switch to operate the relay then would that work as per below

Description

I would of course rather not have to add another relay but I have several of these switches and dont want to have to change them all

[Edited on 17/11/16 by tims31]

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Originally posted by 02GF74
No. If switch is swithed earth, then how can the led light up.

Lets start at beginning. How many pins has the switch. When switch is on, which pins are connected together. What is each pin connected to,

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You have u2u

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Originally posted by 02GF74

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Originally posted by 02GF74
No. If switch is swithed earth, then how can the led light up.

Lets start at beginning. How many pins has the switch. When switch is on, which pins are connected together. What is each pin connected to,

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who haven't answered these questions. photo shows 2 contacts yet your wiring diagram for the switch shows 3., Further more the last circuit diagram you have drawn shows that the led is earthed internally - how can that be without a third contact?

when the main lamp are turned on, you get 12 V - that is the supply you need to switch using your led switch for a relay to switch the fog lamp

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Originally posted by turnipfarmer
You have u2u

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Originally posted by tims31

I dont know what you mean by 'you get 12 V - that is the supply you need to switch using your led switch for a relay to switch the fog lamp'?

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Originally posted by turnipfarmer
I'm only an amateur, & all I can say is that my rear fog is wired exactly as per Tims31 diagram. It works fine & passed IVA.

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Originally posted by tims31

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Originally posted by 02GF74

quote:

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Originally posted by 02GF74
No. If switch is swithed earth, then how can the led light up.

Lets start at beginning. How many pins has the switch. When switch is on, which pins are connected together. What is each pin connected to,

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who haven't answered these questions. photo shows 2 contacts yet your wiring diagram for the switch shows 3., Further more the last circuit diagram you have drawn shows that the led is earthed internally - how can that be without a third contact?

when the main lamp are turned on, you get 12 V - that is the supply you need to switch using your led switch for a relay to switch the fog lamp

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Hi, I answered the questions last night,

The switch has three pins

1: Load
2: Supply
3: LED -linked to supply pin

When switch off pins 2 and 3 connected (Load-earth)
When switch on pins 1 and 2 connected (supply-Load)

The photo was taken from a bad angle, the one below shows the three pins with the wiring diagram for it below

I dont know what you mean by 'you get 12 V - that is the supply you need to switch using your led switch for a relay to switch the fog lamp'?


Description

[Edited on 17/11/16 by tims31]

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Therefore it will not work in a switched earth setup, unless you can strip the switch down and reverse the polarity of the led and then give it a 12v feed where it would normally be earthed.

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Originally posted by 02GF74

quote:

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Originally posted by tims31

I dont know what you mean by 'you get 12 V - that is the supply you need to switch using your led switch for a relay to switch the fog lamp'?

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Aplogies, i didnt spot your reply.
So 3 pins, that makes more sense.

The above, i thought fog lamp is only allowed to be on when main lights are on, it cannot be switched independently. If not, ignore that comment.

There've lots of replies, you still needing help or have sorted it?

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