That SOT cable plugs into your oem harness, the one that normally plugs into the radio, it daisy chains them.
Look at the oem connector and just check you actually have speaker wires going into it. If you don't you then you have an amp and you need to have a rethink.
the oem harness, the one that normally plugs into the radio has 3 plugs two up and down side by side the right hand one 8 wires the left ony three and a top right hand corner plug with smaller wires aprox 4 i know that some of these work with
steering wheel controls i am new and have not learnt to upload photos sorry
I'd doubt its the parrot box, they rarely go faulty in this way. This sounds like you have an amplifier from the description (or the speaker wires aren't plugged in via the parrot)
if you want to find out if its the parrot box, unplug the speaker connection and put two of the same coloured speaker wires from the plug coming out of the parrot box across any old car speaker. you should get some kind of sound out (alternatively go and visit your local friendly parrot dealer who should have a display stand you can simply plug your box into to try it.)
guess what 2 wks and could never resolve the problem of no sound from the parrot kit
,,,,,, tried a new parrot box and sound came on straight away.
Thanks for all the help i got ----i learnt quite a bit and got sorted in the end