I have such a problem, I recently bought a version 9N vw polo 2004. In the car during the purchase was mounted a radio that was encoded and the car salesman added a second radio to the car that is not encoded and that I could take. On the previous radio Code was displayed ----- whether the power was when it was bought in a few days I did not pay attention to whether something was displayed or not. After reaching home and wanting to connect a new radio, I noticed that nothing was displayed on the old one, I thought maybe the fuse went. Today I finally got to it and the situation looks like this. In the car I put another radio that works in another car and everything is ok, the radio in that car also works (it is, of course, coded but gets power), the fuse is good, a colleague checked with a multimeter and the power supply is both on the fuse and on the cable and on ISO cube end, approximately 14V. I also changed cubes, everything is fine. I have no ideas what it may be wrong, I understand that it did not work long but still that week when I watched it everything was ok. I attach pictures of cubes although I do not know if it will work.
You have two pros in the ankle, one is a constant power supply and the other is an ACC power supply, I don't remember what the colors are, but check the weight with the meter. Turn on the ignition switch, find two pros and replace them Preview image replace in cube II 7 of 4
In the Iso cube you can have three different power supplies, one plus permanent, the second after ignition and the third which appears after turning on the lights and board illumination so-called illumination. The permanent plus is protected by a 5A fuse. You have everything in the description of the fuses. In addition, often non-factory radios have minimally different connections in the black cube and sometimes the assembly places pins in places compared to the factory radio. So you need to check the fuses and connections in the black cube in the brown you have vertical speakers. The sure thing about the car was some nice radio and swapped cables, so the trader put the hole in the hole.
And you checked if you have plus on pins 4 and 7, it is possible that this radio coded does not have ACC and only needs power from one pin, which with this second radio you need power from two "12v and 12v pins on the ignition switch for proper operation ACC (unless you want the radio to play regardless of the position of the ignition switch, then you bridge pins 4 and 7)