Both, really, but the smaller rear lights have very little electronics built in and rely on the front light and its capacitor to store charge, which won’t work say if you’ve mismatched brands (B&M front and Supernova rear, for instance, like mine).
Edit, reading your second comment it should work really, have a play with the connections perhaps?
Yeah, I mean, I have a very similar setup on two other bikes so I don't see what I could've done wrong. Famous last words. No, the Germans did it wrong, for realz.
Both, really, but the smaller rear lights have very little electronics built in and rely on the front light and its capacitor to store charge, which won’t work say if you’ve mismatched brands (B&M front and Supernova rear, for instance, like mine).
Edit, reading your second comment it should work really, have a play with the connections perhaps?