Tracks 197 to 210 describe the networking of the main and reversing light switches.
In the cockpit, there’s the multi-contact main light switch (E1) incorporating instrumentation dimmer (E20) and a small lamp (L9) to help find it in the dark. There is quite a big of redundancy in the switch as it implements logic to meet regulatory requirements. We only need to detect which of its 3 states it’s in; off, park or main lights.
“Park” is detected by the closing of connections between terminals 30 and 58. “Main” by the closing between X and 56. Driving L9 also needs that connection at X as well as the nominal “chassis” terminal 31.