So, as i have learnt tonight - the harness on the stock head unit is very tight. Once the clips are released that hold it into the dash, it can be moved about 5-10cm before stopping because of the wires snagging (This is after removing screws at the bottom and the 10mm bolt into the side of the head unit driver's side) The first wire to remove is the A/C wire at the bottom. This one is quite easy to feel and remove, as it's only at the bottom just above where the cigarette lighter was.
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The second one to try and remove is the big one on the right hand side (as looking from the driver's seat). I've included the locations of where the wiring harness sits as default below, and also the rear of an S1 and R3 head unit seperately. In my car, this big cable was held to the HU by a cable tie right where the cut black plastic is on the middle of the rear R3 HU photo - above the centre screw. The release tab is easier to feel on this big connection, and it doesn't take much force on the release, but does take force to remove out of the HU (or mine did hah, it got my knuckle here
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S1 RADIO.jpg
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These next two photos show first, the position of them by default, however the second shows where they can be moved to. After the first ac connection is removed, the HU can now move up, and the harness can (hopefully) be manipulated to above this plastic piece on the second photo. This is likely easiest when the big connector is removed as it will allow more length on the last connector (which the release catch is a PITA). If the harness is above that plastic, the HU will slide out enough that it can be rotated carefully through 90 degrees clockwise, and i could just get my hand and pliers in to compress the release catch on the last connector and pull the HU out with my other hand. This is the way I did it and managed, although I did scuff my left edge of the dash a little doing this, so i'd suggest covering it or sellotaping some sort of padding there to protect.
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this below shows the last connector, where the release catch is below the tough plastic in the centre so is not easy to push in. Or at least i found it very trying
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I've got a few improvements and other things to do to my install, so it'll be in bits again before long after i've ordered the extras. Like the red usb c cable hanging out the centre for android auto as a temporary measure. I may look at making an overall guide to the process and i'll take some better photos in daytime this time hah and properly write it up in future. In the meantime if anyone needs details/photos, let me know and i'll try and help as best I can
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