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Iva Fog Lamp Wiring 2014


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So it seems most of the dreaded Fog Lamp threads are rather old now, 2009 or before, and as such don't capture the latest IVA changes that were made. Namely :-


(From M1 Manual v9.00) Section 28

RS4. The rear fog lamp(s) must only illuminate when dipped beam, main beam or front fog lamps are lit (See Notes 3 & 4)


Note 4: Either of the following applies:

1) The rear fog lamp(s) may continue to operate until the position lamps are switched off, and the rear fog lamp(s) must then remain off until deliberately switched on again or,

2) An audible warning, additional to the mandatory tell-tale light, must be activated if the ignition is switched off or the ignition key is withdrawn and the driver's door is opened, whether the lamps in (RS4) are on or off, whilst the rear fog lamp switch is in the "on" position.


There is some vagueness introduced by the wording in RS4 and the use of "or", which can be used to imply that the fog light(s) only have to work when one of the options (dipped, main or front fog lamps) is powered on, however I believe some testers are demanding the fog lamp work in all states and it's probably a case of being overly pedantic about the wording. Either way, it is not difficult to use a pair of diodes off the dipped and main beam feeds to ensure the rear fog works in both states.


My main challenge is around Note 4.


Either a buzzer sounding when you turn the ignition off with the switch still activated, or you make the fog light output latched so that it automatically turns off when the sidelights are turned off, and doesn't turn back on. This is easily achieved with a latching relay *but* the relay requires a momentary button rather than a switch, which is hard to find that matches with my other switchgear.


So it seems my options are to :-


- Change all my switchgear to match and find a momentary fog light button that ticks the boxes (I'm a stickler for it all looking co-ordinated!) then use a latched relay fed from the sidelight circuit.

- Make a buzzer.


Option 2 is sounding the way forward at the moment. Or am I missing a trick?


edit: Oh, and I know about the CBS module but I'll be buggered if I'm paying £36+P&P for a solution!

Edited by brumster
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I used a pair of diodes, no warning buzzer though. Derby test station only seemed interested in the fog light being on with dipped/mains, and not sidelights. If I turn the fog light on then lights off, the fog light will come back on when dipped or main beams are used again.

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I used a pair of diodes, no warning buzzer though. Derby test station only seemed interested in the fog light being on with dipped/mains, and not sidelights. If I turn the fog light on then lights off, the fog light will come back on when dipped or main beams are used again.


Hey Zach - that's interesting, as it seems completely at odds with the IVA guidelines. Anyone else finding this when they get tested? Don't really want to risk it and find I get an examiner who follows the rules :D

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I am working on a project which will satisfy all requirements of that wording.


In other words, to turn off if the main lights are turned off and remain off if they are turned back on.


I hope to be able to produce these for around £15 or possibly less.


I will keep this forum updated on the progress.


I intend to make this into a small black box which will be wired into existing fog light switch gear. In other words, not require a momentary action switch and the LED indicator will only light if the fog lights are ON.

If they go out by turning on ignition or cycling the main lights, you would have to press the fog switch off then back on again to make them work. It should be about the size of a box of matches.


Would people be interested in this ?



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I'll just say now, so you don't get the wrong end later on once you've gone all public with it, but my intention if no-one had a solution was to knock up a little wiring diagram for some electronics components that would effect the same thing and make it up on protoboard. Just saying now so you don't think I am trying to steal your thunder or ruin your (great) initiative. I won't be selling them ;)

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Hi Dan,

I also went through IVA at Derby (in July), I had the attached simple circuit with a buzzer.


As long as the fog light does not come on with the sidelights (dip or main beam only), and there is something to stop the light coming on the next day when the fog has cleared you should be fine.


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The circuit that snowy has demonstrated means you cannot turn the fog lights off independently and only go off with ignition off or main lights off then on again.


I am hoping to build a circuit where you can turn the fog lights on / off with the switch but that also turn off and stay off in a similar manner to the above circuit without using comparatively expensive relays.


... To be continued ...



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Just trying to understand some of the 4000-series logic ICs, I figure these are an effective way of switch the low-current side. I could resort to a microcontroller pretty easily and do it all in code but figured there must be a way to do this with simple DIP-package ICs and some power relays....!

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Mine just passed IVa at Beverley. All you need to ensure is the fog light only works when main or dipped headlights are on. Ie specifically fog light not on when just side lights are on.

My solution was based on the sierra loom and picked up the brown 'earth switch' wire running between both light clusters. A previous post of mine has the detail as explained by an other .....

Otherwise you could use a simple live feed from both main and dip both fed through a diode to power up a relay for the fog ...

Don't be drawn in to a complex fix. You do not need auto off or buzzers.

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Sure, understood. I'm aware of the solutions above, but it begs the question, why are the IVA examiners not enforcing the regulations? Does anyone have any written statement or such that says they are accepting the documented standard? As it stands I fear I'm playing a bit of a lottery when I turn up there with it as documented above (ie. not buzzer or reset when ignition off)....?

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