Brake Pedal Return and Brake Lights.

We assume you compared old and new correctly, i.e. aligned the flanges and saw the hole for the brake pedal was in the same place. If so, most likely your brake switch needs adjusting. You should always loosen it and adjust whenever changing MC and such. Amazing how many people here never figure that out. More commonly, their pedal bottoms out against the switch, which prevents the MC from fully retracting to expose the fill port. That causes worse problems. The switch should only sense pedal motion, not stop it.