Not sure under the service flap area. I’d just poke a tiny hole in the grommet of the firewall (behind the coolant bottle), thread the wires through, then use the grounding post on the left side of the driver foot well (on top of the dead pedal).
the way I am running my wires I would prefer not to have to run more wires then needed so I will just have to look myself. I thought sure with ll the work done by members that someone would have found a place, If and when I find one I will post it for everyone to use in the future
Look for brown color ground wires. Seems like it is good practice to attach to where they attach to, considering the smart has a lot of plastic. (Mine came with fog lights so never really poked around in the area for wiring concerns).