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View Full Version : My Tail Light Mod (Fogs on when hitting brakes)



Fender0122
10-27-2011, 07:42 AM
Hey All,

So I modified these facelift tails for my buddy to make the rear fog lights light up when you hit the brakes. I ended up buying these off of him and had to make a few modifications to work with my 97.5. When I first modded them, I was no longer able to use the rear fog light. After several weeks of fog around here, I wanted that functionality back. This modification will allow the fogs to turn on with the brakes, while also making the fogs still functional if needed.

Why do this? It makes for better visibility when braking and better visibility in the fog and rain.

I had to first make the passenger side light accept a bulb, which only consisted of cutting a whole in the housing where the bulb goes and putting a bulb in.

Next, I ran a jumper from the regular brake lights to the fogs. I realized that with just a jumper wire connecting the two it would make the fog light switch light up every time you stepped on the brakes. Also, if you hit the rear fog switch it would light up the brakes. Here's my solution to both problems: place diodes where the jumpers would go.

https://lh3.googleusercontent.com/-T85Tiy2_htI/TqlYDZ2QSYI/AAAAAAAAAP8/FUHqwfa7T0I/s512/2011-10-26%25252018.35.25.jpg

This is the drivers side panel, you will need to do the same for the passenger side. I have two diodes soldered in each panel. Note the orientation of the line of each diode. Basically the diode on the left allows power to go from the brake light to the fog but does not allow the power to trace back if the fog switch is turned on. The diode on the right allows the power to be sent from the fog switch to the fog light, without the power tracing back and turning on the switch light when brakes are applied. The circuit is snipped under the diode on the right, as well. I am not sure of the exact diode I used, but I will update when I get a part number. You can do what I did and ask for a correct 12V diode at the electronics store. Be sure to sand the soldering surface to get off the aluminized coating to make it easier to solder.

That's all you have to do! Here's the end result:

Lights normally when headlights are on:

https://lh6.googleusercontent.com/-mtNl6l3ypiE/TqlYqDrkeWI/AAAAAAAAAPo/7gVPAhgeSbE/s640/2011-10-26%25252018.43.04.jpg

Brake lights now:

https://lh5.googleusercontent.com/--wwB-4d6P4c/TqlmwyeA2oI/AAAAAAAAAP4/mQTr2BkTKm4/s640/2011-10-26%25252018.44.09.jpg

Lights when fogs are on:

https://lh5.googleusercontent.com/-AdCBhFH0OvE/TqlZI5oE8mI/AAAAAAAAAPs/awZ1NECYjCM/s640/2011-10-26%25252018.43.40.jpg

Happy soldering!

walky_talky20
10-27-2011, 08:15 AM
I'd rather have just the driver's side fog on with the fogs. Otherwise people will just think your brake lights are stuck on. IMO and all that.
But kudos on the mod. I definitely like the brighter brake lights and I really want to do it at some point.

Also, those mudflaps are awesome.

bez101
10-27-2011, 08:27 AM
if i did that here in the uk id be took off the road
fogs are a big no no

Fender0122
10-27-2011, 08:30 AM
I know! Why is that? I heard Jeremy Clarkson say that on Top Gear one time. I personally think they are very useful bc there have been times I cant see a car in the fog until they hit their brakes.

Thanks on the mud flaps, theyre actually just truck flaps from Advance Auto that I painted the audi symbol on

bez101
10-27-2011, 08:36 AM
if its foggy we can use them
same as the fronts we get fucked if we use them in normal weather
sumat to do with ppl behand think were brakeing and thwy brake and cause tailbacks
retarded realy

walky_talky20
10-27-2011, 09:50 AM
Yes, this is why the rear fog should only be a single bulb on the driver side of the car. I agree, when it's like pouring rain or fog or snow, I keep it on. Whenever I notice I can't see the cars in front of me very well, I kick it on.

One thing I've noticed lately is IDIOTS who think daytime running lights are all they need in the world. They are driving in the pouring rain, at dusk, with no tail lights on at all. I'm not sure if they don't realize their tail lights aren't on, or if they just don't care. No amount of flashing my lights at them will get them to turn them on. I've tried time and time again. This is a huge pet-peeve of mine.

SN95Audi87
10-27-2011, 09:55 AM
Yes, this is why the rear fog should only be a single bulb on the driver side of the car. I agree, when it's like pouring rain or fog or snow, I keep it on. Whenever I notice I can't see the cars in front of me very well, I kick it on.

One thing I've noticed lately is IDIOTS who think daytime running lights are all they need in the world. They are driving in the pouring rain, at dusk, with no tail lights on at all. I'm not sure if they don't realize their tail lights aren't on, or if they just don't care. No amount of flashing my lights at them will get them to turn them on. I've tried time and time again. This is a huge pet-peeve of mine.

Seen this plenty of times!