Fog lights wiring

[talrusan]

Hello guys,

I'm thinking of adding two led lights 4 inches to spare tyre cover. And i want to use same wiring of the rear fog light, but I'm not sure that wiring can bear the current of the two led lights. What do you think?

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[erad]

How long is a piece of string? How powerful are the LEDs? If they are tiny little things you will probably get away with the existing wiring (the manufacturer normally puts a little reserve into the product, unless it is something critical like a space shuttle where every bit of weight counts). Since there is only one fog light (often there are two) it is likely that they used the same sized cabling for that light as say for the tail lights where there are 2 and also a number plate light, so the cabling will probably take the load OK.

You can almost certainly get away with adding 2 lights simply because the fog lights should rarely be used and even then only for short times in cooler, foggy conditions. Unless you intend to use the lights as camp lights when they would be on for long periods, the cabling won't get very hot. I added some high level LED lights to the stop and blinker lights at the rear of my caravan. Because I had to run the cabling externally, I chose to use some old telephone cable - it was small diameter and white which matched my caravan. The LED repeater lights probably don't draw much current, but the telephone cable is very light gauge wiring, and I found I had to double up the wires to minimise the voltage drop. Even so, the cable was 5 core, so I used 2 cores for stop light, 1 core for the blinker and 2 cores for the earth return. I would have liked more cable, but that was all I had to fit there. So LED lights do pull some power - it depends on how powerful they are as to how hot the car's cabling will get under load.

[DibbyDibbyDJ]

Not without a separate relay. You could blow your ETACS if you connected it directly

[Mike DiD]

If you replace the filament bulb in the Rear Fog Light with a Red LED Bulb, then all three LED lights will most probably draw less current than the original filament bulb.

[talrusan]

If you replace the filament bulb in the Rear Fog Light with a Red LED Bulb, then all three LED lights will most probably draw less current than the original filament bulb.

I already replaced the original bulb with led bulb, but i still have doubts to add the led lights.

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[talrusan]

How long is a piece of string? How powerful are the LEDs? If they are tiny little things you will probably get away with the existing wiring (the manufacturer normally puts a little reserve into the product, unless it is something critical like a space shuttle where every bit of weight counts). Since there is only one fog light (often there are two) it is likely that they used the same sized cabling for that light as say for the tail lights where there are 2 and also a number plate light, so the cabling will probably take the load OK.

You can almost certainly get away with adding 2 lights simply because the fog lights should rarely be used and even then only for short times in cooler, foggy conditions. Unless you intend to use the lights as camp lights when they would be on for long periods, the cabling won't get very hot. I added some high level LED lights to the stop and blinker lights at the rear of my caravan. Because I had to run the cabling externally, I chose to use some old telephone cable - it was small diameter and white which matched my caravan. The LED repeater lights probably don't draw much current, but the telephone cable is very light gauge wiring, and I found I had to double up the wires to minimise the voltage drop. Even so, the cable was 5 core, so I used 2 cores for stop light, 1 core for the blinker and 2 cores for the earth return. I would have liked more cable, but that was all I had to fit there. So LED lights do pull some power - it depends on how powerful they are as to how hot the car's cabling will get under load.

So if i made new wiring from the spare tyre area to the battery area, will it be an easy mission?

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[NFT5]

Let's backtrack a little here.


If you've already replaced the incandescent bulb in the rear foglight with an LED then is it reasonable to assume that you're looking for more output, i.e. a brighter light? If so, why?


You should understand that the placement of the LEDs will not match that of the filament in a bulb, so, with the rare exceptions of some Philips LEDs the output will now be less than it originally was. Is this the reason why you now wish to add extra LED lights?


Wiring to the rear fog is positive switched. This means that the line only becomes active when you turn on the rear foglight. Sensibly, this resets to off when the vehicle is turned off and restarted. Thus the rear foglight needs to be turned on with each use, i.e. it defaults to off. Although the relay controlling the current to the rear foglight is controlled by the ETACS ECU it isn't actually monitored and is fused only upstream of the relay with a 10A fuse. Thus there is a very high potential for overloading of this circuit.


So, adding extra lights to this circuit is not really a good idea unless total current can be kept well under 10A.


Going back and extrapolating from my earlier question on why you'd want to do this, I would then, logically, presume that it is either for use as a worklight/camplight in which case, as I've outlined above it won't work. Alternately, as extra lighting to the rear when driving. I'd never really considered Jordan as a place of heavy fogs, but there may be areas where this is the case. In such instances, the factory rear foglight is more than capable of providing the additional visibility required in such conditions. It should never be used in conditions where visibility is not compromised or limited because of the discomfort of a very intense light to drivers of following vehicles.



Adding additional LEDs to the rear foglight function will only increase discomfort for following drivers. In Australia that is likely to earn you some flashing and some choice aspersions cast on your character and/or mental capacity. In the Middle East it may well earn you the business end of an AK47 aimed at the back of your vehicle.

[Mike DiD]

The 10 amp fuse feeding the Rear Fog Lamp means you can have ONE HUNDRED AND TWENTY WATTS of lighting. That much LED lighting would blind any driver behind you.

If you use RED LEDs, it will be MUCH brighter than the equivalent filament bulbs. If you put in a WHITE LED, you're wasting most of the energy, because the Red lens filters out the Green and Blue component of the white light from a white LED or filament bulb.

[Keithyv]

To answer the question I severely doubt the very small extra current draw of 2 LED lights would be too much for the wiring or fuse. Especially if you've already changed the standard rear fog light to LED. The overall draw of 3 LED lights is likely to be far below 1 incandescent.

The actual question is why you'd want to wire extra lights to the rear fog light?
Are these extra lights white? For what purpose? Work lights I assume?

[MSF]

A friend with an NS disconnected his Rear Fog light and ran a separate wire to make it come on with the brake lights, Certainly gets your attention when he presses the brake pedal now and as he said - where he lives, he has never seen fog in over 40 years. The Fog light circuit now powers two 18W White LED lights that he uses for reversing and camp set up etc.

This has been running perfectly for about 8 or so years now and no issues..

I have done a similar thing with my NL, (see pic)
Disconnected the TWO rear fog lights (Circled) and they are now connected to the Brake circuit. No issues so far..

I have the fog light circuit sitting there unused at the moment, but I will eventually wire up a rear camp light on a pole off my spare wheel carrier. - I already have two 18W additional LED reversing lamps wired into the reverse circuit.

As mentioned above, the standard circuits are OK as long as you don;t put too much current through them

[talrusan]

Guys thank you all, I'm sorry i think i didn't deliver the right idea. i wan't to add extra two led lights just like the picture. And i was thinking to connect them to the fog light because i don't want to make new wiring and switches. so i can switch them on and off by the original rear fog light.

[MSF]

They should be fine.
A couple of 20W LED's will draw about 3.5 maximum.
The factory 21W Incandescent will be about 1.75 amps maximum

So that gives you a total of 5 to 5.5 amps max..

The circuit is protected by a 10 Amp fuse, so that is theoretically capable of twice what you are asking of it...

[Mike DiD]

. . . . .The factory 21W Incandescent will be about 1.75 amps maximum ...

But until the filament heats up, it will draw up to 15 amps for a fraction of a second. LED lights don't have this inrush current.

If you don't believe me, measure the resistance of the cold filament, then divide 12 by the resistance in ohms to calculate the cold inrush current.

[MSF]

But until the filament heats up, it will draw up to 15 amps for a fraction of a second. LED lights don't have this inrush current.

If you don't believe me, measure the resistance of the cold filament, then divide 12 by the resistance in ohms to calculate the cold inrush current.

Wasn't aware of that, but two things to note.
1. The 10A fuse currently handles it.
2. Reading back through the post - The OP mentioned he has replaced that incandescent globe with an LED anyway.. So not an issue in hindsight..