www.jec.org.uk

I fitted a Nextbase dashcam to my facelift X350. Pretty easy, but as I couldn't find any guides, I thought I'd add one.
There's a "cigar lighter" accessory power point hiding in the glove box on my car, which made it very easy and saved buying any adapter cables. I think some X350 models don't have it, so this won't be as much use.

As the forum allows only 3 pictures per item, I'll have to split it into 3 parts:
Fit the cam with a rubber sucker, and trail the cable up to the edge of the roof lining, and lead it round to the passenger side A post. The cable, and the interference suppressor easily fit.
It may be necessary to get some slack in the roof lining by loosening the fixing screws (Philips head) behind the little plastic covers for the sun visor: and grab handles:

Next, remove the rubber wind seal from the passenger door frame adjacent to the A post. There's no need to remove it all, but don't try shutting the door with the seal displaced or it'll get crunched. Now you can displace the A post trim. Beware, there's loads of gubbins behind it, including a safety strap to stop it hitting you in the face when the curtain airbag goes off. DO NOT TRY TO REMOVE IT. The trim is held in place by one to three plastic spikes that push into collars on the A post.

Thread the cable down behind the trim, replace the trim and wind seal. A bit of fiddling leaves the cable emerging near the lever to open the bonnet. Remove the plastic tread plate across the bottom of the door frame. It's held in by some tough plastic bits that fit into recesses in the plastic cable carrier underneath - a firm pull vertically will remove it.

Now displace the lower part of the door seal, so you can remove the plastic cover over the bonnet lever and other gubbins. That's retained by a couple of plastic pins on the vertical face adjacent to the door opening; the pins point forward. You have to manhandle the cover from behind the lever, and away from the carpet at the back of the foot well.

Open the glove box and remove its contents. Squeeze the glove box tray sides towards the middle, pulling the retaining projections clear of the glove box compartment sides, allowing the tray to hinge past its normal limit.
Do not remove the plastic gizmo on the side by the centre console. It turns out to attach a string to take the weight of the tray and contents; if you release it, there's a whirr and it disappears behind the fascia never to be seen again!

Lead the cable up into the glove box compartment from the front (there's no access underneath), behind the tray, and insert the plug into the accessory socket.

Loosen the retaining screw to the left of the socket, and squeeze a cable tie between the socket and the compartment liner. Tidy up the spare cable with another cable tie, and thread the first one through the second to neatly package it up against the accessory socket. Tighten the screws, and put everything else back in place. All done.