]Hey all, I found this on a USA forum and thought it looked really cool and easy - I might get to it this weekend, if anyone beats me to it, just let me know how it goes
This DIY as is, has been done on all 1st gen 6i, 6s (including hatch backs), and Mazdaspeed 6. But you must have a spoiler with a 3rd brake light.
(Hatchback version of this DIY can be found here.... DIY: Brake Light Mod (Hatchback) 2003-2008 - 6Crew.com Forum)
Here are before and after pics for those who may not know what this mod is.
after
Tools you may need
16ga wire, Electrical tape/solder, Flat head screwdriver, wire stripper (knife in this case) For a noob it would be worth a couple dollars to get the proper tool for wire stripping. I can be found at any hardware store.
1) In order to remove the fasteners use the flathead screwdriver to pop up the center locking mechanism then pull fastener out. Remove all plastic fasteners from top of trunk in order to remove the carpet.
2) Take about 4feet of 16ga wire, strip the one end, strip enough to fold over the end making the wire twice as thick.
3) Find the harness of the running light you want to make a brake light.
Stick the wire in the open slot of the harness.
Give a light tug to make sure it is secure and has made a connection.
Tape this new wire to the other two for more added security.
4) Now take the other end of the wire and run it to the other running light you want to be a brake light and connect the same way you did in step 3.
5) Now, find the harness for the Third brake light that you have in your spoiler.
Much like you did with the tail lights you are going to strip one end of the wire, and stick the wire into the harness. Only this time do not fold the end of the wire over 'cuase you will be sharing the slot this time. Stick the new wire in the same slot as the black and white wire already in the harness. This should be a much shorter piece than what you used the first time. Read step 6 before you cut this piece of wire.
6) Now the other end of the wire you just striped is going to tap into the first wire you ran. In the center of the first wire, strip a small section exposing the wire. If this is too difficult, just cut the first wire into two pieces and strip both new ends. Take the wire from the 3rd brake light and run it to the bare section in the first wire or if you cut your piece tie all three pieces together
Tape up or solder your exposed wire. Tape/secure your new wire to the trunk lid anyway you like for a clean install.
7) Before you put everything back together close the trunk and check that the new brake lights do indeed work.
8) If everything works out good, close it up and go for a drive