Opening the Shimano hub magneto...see how simple it is?

[ampdavolts]

It's completely normal, a standard Shimano front hub "dynamo" (magneto is the more correct term). This version is styled for the presently-discontinued Coasting three speed auto shifting bikes. The Shimano engineers intelligently chose their already-perfected lighting dynamo/magneto, for the purpose of generating the slight power needed to shift their Coasting system. It has no wearing parts other than the normal cup and cone bearings. There are no brushes in a magneto.

[ampdavolts]

quoted from Wikipedia, "magneto", excerpts: Production of electric current from a moving magnetic field was demonstrated by Faraday in 1831...One popular and common use of magnetos of today is for powering lights on bicycles. A small magneto is mounted on the wheel of the bicycle and generates power as the wheel turns...In the inductor magneto, the magnet is rotated and the coil remains stationary.

[ampdavolts]

Quite surely, all hub magnetos will be essentially similar to this design. Though this one, in the Trek Lime (and other Shimano Coasting bikes) is dedicated to powering the automatic shifter computer/motor, perhaps it could be, for fun, employed to make some LED lights blink or flash brightly. I might try that someday, to see if the magneto can handle doing double duty, as I like to ride at night and batteries for blinkies are a bother....