It is technical info for the make up of the components. This is how I would interpret it:
AM1 main - Indicates the circuit (alternator and other circuits)
1.25B - should be the wire gauge, in this case it would be 16 AWG
2.0L - I am not really sure maybe load capacity
I am sure @jonheld, @Malleus or another electrical guru can chime in an correct me if I am wrong and possibly fill in the missing info.