Haven’t got any pictures of it but if you watch this video you’ll get the idea. This is done on the W176 but there’s a bolt in the same place on the W177.Hi,I earthed mine on the lowest 13mm bolt securing the dashboard, about a quarter of the way back up from the fuse board.
can you share any photo ?
as the driver side is on the left... Probably it might not exist a ground bolt in the passenger side