Canon EOS 10S - bc error with locked mirror

While the Canon Elan 7 cameras I fixed in my last post are fantastic, they utilize IR light to count sprockets. This is a problem for IR sensitive films that are actually IR, like Kodak HIE, or Ektachrome Infrared (Aerochrome). This would cause the film to fog. Additionally per , there is a hole in the pressure plate  for a date counter which may lead to weird issues in the film. I needed a camera that could take my Nikon F-mount Coastal optical 60mm lens, so I picked up a used EOS 10s on ebay for 25$. After building a battery (It takes a 2CR5), I went out for a shoot, and to my dissapointment, I couldn't get the shutter to fire with the Coastal-opt and an adapter! The mirror would go up, and there would be a "bc" error on the LCD:

bc error on EOS 10 LCD

The camera would fire however if I untwisted it a few mm from locked. I discovered a pin inside the lens mount that doesn't exist on any other Canon cameras I have. The adapter was pushing on this pin, and when it was pushed, I got the error:

I found a reddit post: that suggested grinding away a section of the adapter. I did it, and wouldn't you know it, it worked great! So if you get a bc errorr on an EOS 10S with a Nikon adapter, because of this detection pin, give this a shot! (keywords!)