Disclaimer: I do not know what the legalities of this mod are in the UK and in other countries. Please ensure that this does not violate any local laws before following this guide.
The 5-brake mod is as it says on the tin, a pretty simple wiring mod to light up the rear fog lights simultaneously with the brake lights, as well as allowing you to selectively use both rear fogs independantly when needed in foggy conditions. A simple switch allows you to turn off the mod when desired.
I’ve noticed that there are a few 5-brake light mods on US forums for various VAG vehicles. Most seem to be rather complicated but one fairly simple approach which I adopted for the Fabia vRS seems to work really well.
You need both rear fog lamps to be active, which on the Fabia is a simple matter of running a jumper wire 14-16 gauge from the empty terminal of the left hand side rear light cluster under the rear trim to the live corresponding right.
Fog bulb, bulb holder etc are already in place from the factory but there's no actual powered wire present!!! (There are threads on Briskoda on how to do this and you can use a Scotchlok connector on the relevant grey-white rear fog wire to join the powered rear fog to the opposite un-powered one) If you look at the small dark rear light cluster connectors, you'll notice that there is an empty "slot" on the Left side one (RHD vehicle). All you do is run a suitable single wire scotchlok-tapped into the corresponding powered side under the rear trim, strip the bare end, insert into the empty slot and then bend it into a little ball from the other side. A little solder applied to the end before insertion helps to make it stiffer and prevent any corrosion. It's not elegant but works well plus it saves trying to find the crimp-on mini terminal end from VAG.
To do this mod we use two magic items called diodes. These act like an electrical one-way valve, allowing current to flow in one direction easily but not in the other.
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Radio Shack part no. 276-1144 contains the 2 diodes you’ll need, cost me the equivalent of £1. (Specifications: 3 Amp barrel diodes 220A surge/400A peak inverse voltage). Thanks to Mathepac for this UK info: the device code for the diode is 1N5404 , Maplin order code QL84F, price 0.17p each ( 0.27c in Ireland). I'm sure Peats or Radionics will also stock them
14-16 gauge wire, about 1 foot
A crimper, barrel or butt connectors and a soldering iron.
A scotchlok tap-in connector is slick but not essential.
Electrical tape or heatshrink tubing with a hot air gun
What you do is solder the diodes and the wire as per the picture below (the silver rings on the diodes indicate the direction of current flow, like an arrowhead):
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As you can see, current can flow to the fog lights either when the brake is pressed or when the fog light switch is on. It cannot flow in reverse (so no brake lights on with the fog switch or the fog light lamp on the dash illuminating every time you press the brake pedal).
Disconnect the battery or pull the relevant fuse (I didn't....)
After preparing your "mini wiring loom" you pull away the carpet trim at the rear to access the rear light cluster (Driver's side). Use a screwdriver to gently raise the tabs on the connector and slip it off. Pic below shows mini harness ready to crimp in.
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It helps to have SWMBO or a mate in the driversseat plus a small 12V lamp on a couple of wires or a multimeter to positively identify the correct connector wires before you start cutting! (The rear fog wire was grey-white and the brakes red-black on my Middle East spec vRS).
Then you cut the foglamp wire before the rear harness + jumper tap to the other foglight and crimp in the wire ends as per the picture; tap the remaining end into the brake light wire with the scotchlok connector. You do not cut the brake light wire at all. Diagram below shows the wiring, note you can insert almost any simple on/off switch to turn off the mod when needed e.g. for the MOT.
Hopefully this will decrease the likelihood of tailgaters ramming me from the rear courtesy of my 312mm brake upgrade! Total cost, about £1 plus some odds and bobs I had about!