I want to use my fog lights as an extra pair of brake lights when it's not foggy so I have come up with the following solution. The theory is that it should enable the fog light to work independently when required (when the fog switch is pressed) without back feeding to the existing brake light.

Can anyone see any problems?
What type of diode do I need to use?
Rescued attachment Brake & Fog Light.jpg

fog lights have to be a certain distance from brake lights, nut sure what it is though (300mm?)

I think that should work, one thing that does spring to mind is you may also be supplying the fog warning light switch on the dash and lighting that every time you put the brakes on.

It may be a MOT failure if this happens as I believe the light must only be on when "FOG's" are on.

I have an LDV that had an interior light on the fog switch so glowed at night and a keen MOT informed me it would fail. You could always use another diode to stop the voltage going back to the switch!

Cheers

Adrian

100mm

quote:

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Originally posted by dan__wright
fog lights have to be a certain distance from brake lights, nut sure what it is though (300mm?)

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Rescued attachment Rearlights3.jpg

something like a 1n4001 should do it,

as said another between the switch and fog light should stop the dask warning lamp coming on

hth

Ray

something like a 1n4001 should do it,

as said another between the switch and fog light should stop the dask warning lamp coming on

hth

Ray

quote:

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Originally posted by AdrianH
I think that should work, one thing that does spring to mind is you may also be supplying the fog warning light switch on the dash and lighting that every time you put the brakes on.

It may be a MOT failure if this happens as I believe the light must only be on when "FOG's" are on.

I have an LDV that had an interior light on the fog switch so glowed at night and a keen MOT informed me it would fail. You could always use another diode to stop the voltage going back to the switch!

Cheers

Adrian

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Rescued attachment Brake & Fog Light2.jpg

yep, should work

Ray

Excellent, another cunning plan to stop tailgaters

quote:

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Originally posted by RazMan
Excellent, another cunning plan to stop tailgaters

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I usually find a good dab on the loud pedal gets rid of them

Drop down no. plate and gun barrell poking out

My tintop has "variable intensity brake lights".

Under normal braking just the 2 brake lights come on. If you throw down the anchors then the tail and fog lights are also turned on so your plan must be legal.

having the fog lights come on with the brake lights is going to be really annoying for people behind you. fog lights are bright and annoying enough when idiots leave them on 3 weeks after the last time it was foggy let alone having them come on every time you brake. not a good idea IMHO

a lot of the legislation about fog lights came in after people got pissed off with idiots who connected them together with brake lights, and they always seem to be the ones who don't know how to use the handbrake in traffic queue's.
Just don't do it, please!

I can appreciate what you are saying and maybe I should revise my plan a little. I know how irritating it is to follow a car with foglights switched on in the rain.

I will look at making the fogs dual brightness and just have them as an extra pair of tail lights (at the lower brightness level of course) but the fogs (brighter level) can still be switched on when required.

I quite like the variable intensity idea though It must need a two-stage pressure switch which is probably as rare as hens teeth.


[Edited on 26-9-07 by RazMan]

bear in mind a diode will have on average a couple of volt drop across it. This might in fact be helpful to you...

Doides normally drop 0.7 of a volt across them. IIRC.

Raz,

A nice bright led pinboard display with a few choice messages preloaded?

Obviously all keen to get a close look at your paint finish...

All of my lights are LEDs so I am not sure how that will change things.
Come to think of it, if I am only going to have the tails switched on (using the brake part as the fogs) I won't need any diodes now.

It simplifies things a bit
Rescued attachment Brake & Fog Light3.jpg

Raz,

What do you want to do - Just have effectively two pairs of brake lights? (As you've sketched) Have the second set come on when you press the brake pedal hard? (a two tier pressure switch) or where you are braking hard? (could use an inertia micro-switch???)

Neil.

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Originally posted by westf27
Drop down no. plate and gun barrell poking out

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I can not see a problem personally with having a third brake light. Many cars have another 21 watt light stuck in their rear window.

There are enough of those LED strip lights around could you not mod and build one in to the rear spoiler or rear window area.

Adrian

quote:

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Originally posted by AdrianH
There are enough of those LED strip lights around could you not mod and build one in to the rear spoiler or rear window area.

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now I'm confused.

first diagram shows fog lamp coming on when brake is pressed and meets the criteria of "wanting to use my fog lights as an extra pair of brake lights when it's not foggy"

With the addition of the second diode to prevent switch illuminating, it will work. As you have LEDs lamps, 1N400x diodes wpould be enough to handle the current.

You can put two, three or more diodes to lose some voltage so make the fog lamp
dimmer but as you now tell us the lamps are LEDs, they may not work if the voltage is too low plus without knowing the internal lamp design, they may be wired up internally to give constant brightness over a range of voltages so voltage droppping diodes may not work as inteneded.

The second diagram now shows fog lamp being used as extra tail lamp so no longer meets the original requirement. Any additional diodes don't come into play not because the lamps are LEDs but because the wiring of the bulbs is separate. (the fog lamp now is a two element bulb whereas previously it was single).

The second digram would work to make fog lamps come on with tail lamps.

Thats the way my brain goes sometimes - sorry to confuse you.

To clarify, after it was pointed out how annoying it can be to have fog lights used as brake lights I decided to use them as tail lights instead - extra night visibility is good thing in such a low car and my existing tail lights are rather small. I have a spoiler mounted brakelight too so maybe five brake lights is a bit excessive

The fog light and tail light 'bulbs' are dual brightness LED jobbies so I can mix and match to suit the requirements.

hth

one q. what makes your brake light different to the fog light?

I think on tintops the same bulb wattages are used but the fog lamp, when on, is brighter due to the lens used, or am i way off the mark?

Thats partly why I decided to go for the tail light option. The lense of the fog light is a little different but by changing the position of the bulb I can alter the focal point of the light, making it a little more diffused and less 'pointy'.