Hello, my name is XXXXX XXXXX I will be halping you today.
You are correct, what was on A on the old keyswitch goes to I on the new keyswitch. The difference is on the actual Johnson made keyswitches(which your old one was), they call it A for accessory. On the aftermarket/universal keyswitches, they call it I for ignition. But it's the same thing.
That should do it, but if I missed anything feel free to ask.
Thanks in advance,