You are right, the empeg does not go in steps like your mirror does.

The empeg's display dimmer is either off or on, and it decides which based on whether there is voltage on the illumination-sense wire or not. It's either dimmed, or not dimmed. You can adjust the brightness level for either state, but nothing in between.

So, whatever your car supplies on the illumination wire, that's all the empeg's got to go on.