It's an often told story about Apollo 12 getting struck by lightning, crippling the command module in flight and John Aaron in mission control figuring out the exact switch to flip to fix the stricken vessel and save the day. It's an understandably popular story, but the details are never quite right, so this is my attempt to explain what exactly went wrong and what problems SCE-to-AUX fixed. Here's a few of the references I used to understand what happened: Apollo 12 Flight Journal https://history.nasa.gov/afj/ap12fj/01launch_to_earth_orbit.html Apollo 12 Mission Control https://history.nasa.gov/alsj/a12/A12_MissionReport.pdf Apollo 12 Saturn V Performance https://history.nasa.gov/afj/ap12fj/pdf/a12-saturn-v-fer.pdf John Aaron Interview for NASA Oral history Project https://historycollection.jsc.nasa.gov/JSCHistoryPortal/history/oral_histories/AaronJW/AaronJW_1-18-00.htm Apollo 12 Technical Debrief https://www.hq.nasa.gov/alsj/a12/a12-techdebrief.pdf Apollo Command Module User Manual - Telecoms Subsystem http://apollo.josefsipek.net/ApolloProjectOnline/Documents/SMA2A-03-BLOCK%20II%20Volume%201%2019691015/aoh-v1-2-08-telecoms.pdf Analysis of Apollo 12 Lightning Incident https://spaceflight.nasa.gov/outreach/SignificantIncidents/assets/analysis-of-apollo-12-lightning-incident.pdf Scott Schneeweis Collection of Apollo Hardware: http://www.spaceaholic.com/index.php/Detail/Object/Show/object_id/42