Right, in your use case you're only going to get 7 maps, you must reserve one map for "fallback", ie. low octane.
The switches I know to work perfectly are
B-11 and B-14 that switch to ground, I tried using D-1 but had a bad experience (this signal goes live when the engine is cranked, triggering all injectors firing at the same time).
As we know B-11 and B-14 to be good, I would try the next GND switched pin which would be B-16, or if that's in use, try C-2.
As for actually switching between those maps, you could have 3 switches to select between the maps, but that's clumsy and easy to get wrong. I started to look into either a
rotary binary switch or a microcontroller such as an ATMega85 with a LED output to indicate which map was active, maybe there's an idea there for you? :)