This afternoon I replaced my cars build-in radio (Sony CDX-S2050 for a Polarlander JSD-520). Everything works fine except for storing presets such as radio-stations and the clock. It stores as long as the key is in the cars ignition.

As all the cables I used were brand new, I assume that all of them are working fine, so my conclusion is that there must be something wrong in the way I've connected them. I noticed that there is something strange in the wiring from my older radio.

The wiring diagram tells me that the yellow wire is used for the continuous power supply (Battery) and the red wire is used for the switched power supply (Ignition). But both of them are reversed connected on the ISO-harness. In other words: The yellow cable is connected to the red wire (A7), and the red cable is connected to the yellow wire (A4).

My car (Volkswagen Golf MK4) never had any trouble saving presets, so the wiring for the old radio must have been correct. Perhaps the ISO wiring in my car is wrong? That's why I would like to know if it's safe to try and reverse the wires the same way on my new radio, or would this cause a short circuit?

Old situation: Sony CDX-S2050/Volkswagen Golf MK4 wiring Sony CDX-S2050/Volkswagen Golf MK4 wiring

2 Answers 2


It won't cause a short circuit. Either your radio will always have power (if they are backwards after the swap), or it will work like it's supposed to (if they are correct after the swap).

There's a quick test you can do in order to determine if they are currently backwards or not. Grad a multimeter, set it to 12 VDC and get a voltage reading from both the red and yellow wires separately (find a good ground). Whichever wire gets you 12 volts with the key off is your constant power. Turn the key to on or accessories and repeat the test to confirm you are getting power on the other wire now.

  • Thanks for your confirmation. I just switched the yellow and red wires using a bullet connector and everything works fine now. Commented Sep 24, 2016 at 8:01

According to Wikipedia on the ISO connectors :

On some cars the +12V Ignition and Battery positions are reversed, such as later Volkswagen Group cars, Peugeot 106,Vauxhall Astra, Citroën C3 some JCB tractors (made in UK).

So this is a common problem, not just yours.

Since both cables have already been swapped, just undo the changes. This is perfectly save, as stated by the other answer, just make sure red and yellow really are switched and permanent 12V.

  • 1
    Thanks, I should have come across that but I've totally missed it. Although I've already solved my problem, I'm quite sure that this will help others! Commented Sep 24, 2016 at 8:42

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