Bedford TL 750 warning buzzer....brake fluid level?

Hi, I have posted a couple of questions about the fact my warning buzzer wont switch off and assumed this was to do with the air pressure (even though it goes to 8bar and holds) I have been checking round the truck and checked the brake fluid and it seems very low/empty. I have recently had a new brake actuator fitted and wonder if they would have had to drain the fluid and maybe not filled it up enough or maybe there has been a leak? Would this cause the warning buzzer to stop on? and if so will topping up the fluid stop the buzzer?

regards