iluvathar:
But I need the voltage divider to read the signal, that is 12 V and 2 A.
If you want to be able to detect the presence of a 12v signal with an Arduino I/O pin then a voltage divider will work. If (as would be normal) the voltage divider uses large resistance values the current will be tiny - just a few milliamps.
Just make sure that even if the voltage temporarily rises above 12v that the output of the divider can never exceed 5v. Using an opto-isolator in place of a voltage divider avoids that risk.
If you wish to measure the amount of current flowing in the 12v circuit then things are significantly more complex. But let's hear if that is what you want before providing unnecessary info.
...R