Whats a brake switch and how can I test it to know it's not working? Many people have this problem when they do a H22a engine swap with auto tranny, they can't get out of park and the D4 light doesn't light up. It's all with the TCU. With the problem that people(including myself) can't get out of park, I need to know which wire to connect from the tcu to the shifter position. About the D4 light, it's not dead because when I put back in my accord tcu, it lights up fine.