I don't know if it's been said here yet, so I'll give my advice anyway.
If you buy your D3 used, you may have to reset it to the factory setting to make this work. I tried it several times, and still got the "brake wrong" message, until I reset the unit. Also you really have to make sure the mute wire is all the way in the wiring harness. A super small screwdriver (as mentioned here) works great.