what are the differences between the mid and hi series BEM??
as far as i can see is its just interior light dimming/fading
also are they interchangeable between models??

nothing? wow

BEM containers immobilizer code and cannot be interchanged without reprogramming, if you do install an unpaired BEM the car will not start.

There are 2 options to fix that, that I know of

- Reprogram the ECU to remove immobilizer (SKR can do this).. but you reduce security of your car
- Swap all 3 components - ECU, BEM and Key Barrel

i know about the immob thats no issue for me
but as for model to model im guessing its possible but need to know the actual differences

Main thing that I am aware of is the slow dim int light, so far with my hi series BEM I have not found any other features the mid series does not have