Mercedes CLS350 - Switched 12v for Thinkware Q800 hardwire install

[AlanFM]

Hi All, Thanks in advance for any help you can offer.
I have a Thinkware Q800 pro, which I fitted and later removed from my old BMW. it worked perfectly there.
I have tried to install in my new car, 2019 mercedes cls350, but it has Keyless Entry, so circuits I would have previously used and assumed were dead while the vehicle was locked, are now constantly live.
I have found a good grounding point, and a good constant 12V in the passenger footwell fusebox, but all circuits there seem to be constantly live so I cannot find a switched 12v supply.

Does anyone have any experience of hard wiring in this vehicle, or advice on how to find a switched 12v without ripping the whole vehicle apart?

I'm considering a work around, by purchasing an external battery which looks to be wired just to constant 12v and then grounded, so overcoming the issue. But its a last resort as getting batteries shipped to Ireland is difficult and buying local generally involves the typical irish price multiplier, seeing me pay circa EURO400 for a $200 Battery.

 

[AlanFM]

As a follow up to this, I have found an OBD2 connection kit, which looks like it will circumvent the issue entirely. Anyone used these, and what do you think?

 

[egonvdv]

I have an E-class,so might not be the same but :
in the trunk there should be a fuse panel with 2x 15v fuses for the cigar sockets
these switch off when engine off (might take a minute or so)

 

[arcticfire]

I wouldn't be keen to power via the OBD2,

The F30 BMW I had could take between 10-20 minutes to shut down some of the circuits, it could be similar for your Merc? The Jaguar I had didn't have any switching fuses, but the 12V sockets (cigarette lighters) did switch off but they used a shared fuse, so I spliced into the 12V socket in the boot and also wired in an inline fuse for extra protection. If you have no luck with any fuses you could also try this.