........... I think the photo does not show the U clamp and 2 nuts,

this usually mounts at the diagonal rear frame tube by / under / below the side cover. left side. it's usually too LOW for my liking as designed. a heated gear cord could e too long, Not long enough, drag by your boot, drag into the rear wheel if not careful.

personally I do not like powerlet sockets. I'm a 2 prong trailer plug weather proof type and have 3 mounted on my R90SRS. I make the corresponding plug into a have dozen different adapters to connect to my tan bag harness, any harness i have for the rear panniers, any type of heated gear / or having an adapter for a COAX type 'N' plug for other type heating gear. i installed my covered outlets up high where I can get to them easily.

Harry, thanks for your reply.

I understand what you're saying, but I'm restoring my bike and trying to keep it somewhat stock. I'll probably rarely use the outlet except to trickle-charge my battery.

Would love to see a photo of the bracket mounted on a frame.

It's been a long journey, but I received a dark, blurry photo this morning that I was able to enhance in Photoshop and figure out exactly where the mounting bracket goes.

I mounted the bracket this morning. Here's a photo in case anyone else needs to know in the future.
With the BMW angled bracket, it makes a nice clean install. FYI, that's a flip-up weather cap covering the socket.