Fuse box diagram?

Those little pictures on the fuse box lid ... is it just me or are several pretty cryptic? I can't tell what some are ... any have a diagram that actually says what each one is? In particular I'm after the fuse that runs the power outlet. (Which is to solve a problem I'm having w/ a USB port that is experiencing power fluctuations from the engine ... hoping if I tap into this connection it might alleviate that issue)

I have the Roadster.

No it ain't just you.
its very cryptic.
I think there's an explanation in the service manual.