Yeah, sorry about the lack of paragraphs. I'm usually much better at it than this. I was a bit panicky that's all.
The switch you mention is normally closed and allows 12v to be detected if it's being powered in the car. When the plug is inserted it breaks the contact and 12v doesn't get through to whatever is responsible for detecting it (I'm pretty sure this is how it works, I'm sure Hugo will correct me if I'm wrong). As you say, I'm half way there with the link I've put in but I've obviously put it in the wrong place for full functionality.
I thought about doing some side by side tests with my Rio MK2a but they've changed the PCB layout in this area so that's a dead end. I'm going to have another look at it tonight to see if I can get a proper fix.
The track that Hugo fixed for me was the one that leads from this switched terminal on the socket to the bit that senses whether it's in the car or not. My biggest problem is that most of the tracks are hidden within the PCB and aren't on the surface at all. This makes it impossible to trace anything without either an X-ray machine or a circuit diagram.
I've also noticed that (contrary to my earlier beliefs) that since I've put the link in it isn't working correctly in the car. It ignores the ignition switch position. I'm sure it didn't do this when I tested it last night
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Thanks for your help