You need to make sure that the yellow and red wire (on your aftermarket harness) corresponds with permanent 12V live and Ignition 12V on your cars wiring ISO connectors.
You may have to push the pins out on your aftermarket harness and swap them over so they correspond. It sounds like you are connecting the plugs without the pins corresponding. It dosent matter if swap the yellow and red wires over if there is no feed in the ISO plug to marry up to nothing will change. In other words you have to make the aftermarket wiring harness suit the car wiring. Also make sure you identify the ground wire and dont short anything to earth. Check it with a voltmeter

 

Thanks for the prompt reply. The wires are paired up accordingly as in each male pin is match with a female one of the same color. The stereo fitted in the car has an adapter fitted with those interchangeable plugs for the red and yellow wires.
So unless I got lost in translation somewhere I'm pretty sure the swap I did was done correctly.
My initial thought was that the constant live wire was not working for some reason as the radio still turns on when the ignition is on regardless of which way the wires are connected.
But I will check the ground tho and see if the issue is there and also try to get my hand on a voltmeter to see if everything is working as it should.
Thanks again for your help!
Much appreciated!

 

Sometimes you need to swap yellow and red

wbr

 

From what I've read, later multiplexed 206s might not have a permanent +12V line in the plug (mine from late 2003 has it) and would require it to be brought in from elsewhere for an aftermarket HU.

I'd take a voltmeter and (once the BSI has gone to sleep, a couple of minutes) check if there's a constant +12V present in the plug. Would require waiting a while in the car with doors shut etc...

 

There are three combinations to have the wires on the Sony BT range. Have a look at your install instructions.