912iS not charging

First question. Did you run it up to 2500 rpm for up to 5 seconds to allow the 2nd generator to come on line?

In order to properly diagnose this, you would need to extract the ECU data! 

Since it is a Kitfox, have you talked to John Mcbean in regards to this issue?

The fuse description is in the Rotax Maintenance manual that you can lookup by clicking on this link here - https://www.rotax-owner.com/en/support-topmenu/engine-manuals#912-i-series-engines

It can be found in section 76-10-00 Page 39

https://www.rotax-owner.com/manuals/MMH_912i_Series_ED1_R3.pdf

From the Rotax 912iS maintenance manual

The internal generator has two isolated coils integrated (individual generators). During the starting operation, the EMS system is powered by the battery. With sufficient speed generator B takes over this function. After the EMS system check, generator A takes over the supply of the EMS system (engine), if the switching threshold is exceeded. Generator B is then used to supply the aircraft instruments and for charging the battery. While the engine is running, the generator B can be used for the aircraft instrumentation. • Generator A 14.2 V/16 A (220 W nominal capacity at 20 °C/68 °F) • Generator B 14.2 V/30 A (420 W nominal capacity at 20 °C/68 °F)

ATTENTION If generator A fails, generator B takes over its functions. The airframe electrical components and the instruments will be supplied by the battery. The battery will no longer be charged!

ATTENTION If generator B fails, the battery will no longer be charged. The engine still runs on generator A and the instruments will be supplied by the battery. The function of the instruments depends on the state of charge of the battery. The charging of the battery from generator B is not monitored by the EMS. An ammeter has to be provided by the aircraft manufacturer according to the latest requirements.