car radio wont power up

[ronhud]

I have a 2009 Multispace diesel 1.6. The original radio was replaced some years ago with a Sony Stereo which suddenly stopped working. I used a multimeter to confirm that 12.5 volts was being delivered to the final connector and checked the fuse in the radio was ok. No life at all so I bought a low cost Bosskzi radio. This does'nt powere up either so I am guessing the radios are ok and I am missing something in the vehicle. I attached my multimeter to the yellow and black wire terminals and get 12.5 v so I assume that earthing is taking place via the black wire. I also have the aerial plugged in.
Can the red ignition wire have anything to do with it. Something causing it to keep the radio without power irrespective of the ignition being switched on.

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[SlugButter]

bad ground maybe.

 

[ronhud]

Thanks for the response I have been told the red wire is the ignition wire and the one needed to power the radio. Checked it and no power so hopefully its a fuse.