Adding Turn Signals to The '5 Light' Brake Light Mod on an A4

I decided to add my turn signals to the additional brake lights that I had already installed a while ago. Or maybe it's the other way around -- to add the additional brake lights into my rear turn signal circuit. There are lots of links to various write-ups of the original '5 light' mod on the forum here; this just allows one more handy option.

Here you see the original jumper that I made, from the top position (the stock brake light bulb) to the position that would have been used on ROW cars.



Here you see representative components, not to scale, that you'll need to do one wire (obviously you'll need two wires to do both sides of the car).



The diodes have a small grey band on the down side in this photo that will go to the '5th. brake light' bulbs. I paid 61 cents today for 8 of them (I have 2 Jettas to do).

Here you see the wire, the terminals, and the diodes assembled, and about to be heat shrunk. The diodes allow power to go to the bulb from either the turn signal, the brake, or from both, but not back in the other direction. When the turn signal is on, the extra light on that side blinks, when the brake pedal is depressed, that bulb will go solid, without regard to the turn signal state. The turn signal bulb is unaffected.



Here you see a blurry photo of the completed wire assembly ready to be connected into the VW tail light bulb assembly. Sorry for the blur.



Here you see the completed jumper with internal diodes, as it is installed on the VW tail light bulb assembly, ready to go back in the car.



The center unused connector spot contains 3 pins, and is labeled in tiny letters 31 (ground), and BL/S. Ground is the left pin -- ignore it. BL is the center pin -- the bayonet terminal is pushed onto this one. The last pin (S) is for the tail light (or 'marker' bulb as the reference material calls it). The other side of your car will be strikingly similar to, but the mirror image of, this (as the brake light bulb goes to the outside position on both sides of your car). FYI, as though it matters, this is my passenger side.

Here is the finished result showing the left side turn signal blinking (you'll have to pretend it's going blink, blink, blink) as well as I could photograph it at night. The full result doesn't really come across, and the colors are not true (the turn signal blinks amber, and the additional brake light blinks red). They are the same brightness, as they are both standard 21W bulbs, obtainable anywhere. I'm sure you get the idea.

Did this on Jetta TDI. Looks great at night. Thanks.

when brakes are applied

I take it that the 5th light will only blink as long as the brakes are not applied? Since power from the brake light will keep it on continuously and only your OEM blinker light will continue to flash. Hmmm...... thinking about it now.... this DOES have the potential of looking very cool in action, dual blinkers for changing lanes, then dual stop lights when stopping!!! Dang now I may need to redo my mod that I did today and change over to this. Do you have the specs for the diodes that are needed? Thanx for the idea

Just did this mod last night, fun idea!

I take it that the 5th light will only blink as long as the brakes are not applied? Since power from the brake light will keep it on continuously and only your OEM blinker light will continue to flash.

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Yep, that is exactly what happens. Interesting mix of red and yellow for turn signal while not braking...

Do you have the specs for the diodes that are needed?

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For diodes I used four 1N4002s sitting in stock at my workplace (circuit board manufacturer). These worked fine for me, no issues with the lights while testing them post mod. Thinking about it now, it would be OK to use any of the standard 1N400x series of power diodes... and those are probably overkill. Even so, they are as cheap as any others and are known to work (I used them successfully and I also believe Left Coast Resident used the same style of black bodied power diode).

Sorry to re-birth this thread, however I had a few questions. I did what you have, except I added a line from RF to RF with the diode facing towards the actual fog light (dual reverse lights, 5 brake light, and 2 turn signals. Everything worked but the turn signals - it immediately blew my 10amp fuse. Any idea what caused this? even just trying the turn signal alone it blew.

Is what I'm trying possible? I took out the turn signal portion form BL to the RF fog light portion, and it all works as I wanted it to. Dual reverse, 5 brake light. I only tried on one. I just finished up the second light just as I left the first one after removing the double turn signal function.

Yay. It works on the drivers side too. Looks pretty damn sweet and a lot brighter backing up now. Now if I could just get the dual turn signals!


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I found even without the mods on, my drivers side, with no DRL's or lights on, upon turning on the turn signal only lights 1 bulb for the turn signal lamp. However, on the right side it lights up both the turn signal lamp and the running lamp. What the heck is going on here!?!

Would this confuse the factory flasher relay which is really only geared to run a 4 x 21W bulb load?

There is another optional relay if you have a trailer which will run 6 x 21W bulbs if this is the case.