Hoping this would help someone, I have had camera's in all my cars for the past 8-9 years and have just installed one to my new to me S90:
I fitted a
Viofo A119 I had from a previous car here, note not but up to the centre console as I'd usually do due to the manual advising against it because of the radars etc.
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Using a small pry tool I removed the 8mm bolt cover on the side pillar
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This exposes the airbag, I routed the cable away from the bag so as not to obstruct it in the event of it being deployed, chances are it would just rip the cable but not worth the risk, the airbag is clearly visible and shouldn't be disturbed, the cable slots nicely onto the existing cable management
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Once done I then removed the lower trim to route the cable to the fuse box under the glove box, this needs to be removed in the order marked and comes away easily using the same pry tool
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The lower sill cover has an led so you need to unplug the green connector (squeeze and pull)
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This can then be removed and placed out of the way
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Pulling the carpet back reveals the atrociously placed fuse box, this hinges the wrong way around imo and makes un-clipping awkward, I took a photo of this to assist me and another to hopefully help anyone else trying his.
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Earth bolts are plenty but the one below was easy to get to and the fuse I chose was one of the 15amp ones for the heated seats (46/47) these obviously turn off with the ignition. If you are using a power magic or similar then fuse 53 is for the Sensus and is permanent feed
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This is the voltage converter I used, I have bought quite a few o these from
Amazon and they work well
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I added some double sided tape to this so it would stay put in the box, just above the lower plug
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The fuse piggy back is a micro fuse one from
Amazon
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Hope this helps someone as there was limited info online for this and I'm sure it'll be similar across the range where the fuses are under the glovebox.