Seems to be a common place to connect aftermarket electonics in JDM Mazdas. Mine wasn't working the same way. Traced it to a blown 7.5A fuse marked as RADIO. Turned out there was a snakes nest of wires near the cabin fuse box and behind the glove box. Removed everything that was not factory made, thus eliminating short circuit that blew the fuse. Now entertainment and commander knob and all the buttons work, except when you tilt the knob left. That doesn't work. I'll look into it later.