I have a current model Extra cab Hilux and want to put some rear speakers in. I removed the RHS rear panel, found the wires and plug but even with the head unit adjusted to full rear speakers, couldn't get any reading on a multi meter. Also tried a horn type speaker, but no noise. Removed the head unit but couldn't find any loose wires or plug. Where have I gone wrong, or is there something missing in the wiring? Any help would be appreciated, Bob