You say the power light is on, indicating a charging issue, right?
The only technical link between electrical charging and the brake system is the brake booster > vakuum > vakuum pump.
(Well, there might also be a brake fluid level sensor that might turn on a warning light.)
So, my idea is to first make sure the warning light is resolved. *,For this, you need to understand what exactly the meaning of this particular light is and what all might trigger it. * -> you need the service manual.
Isolating the charging system from the brake system by disconnecting vacuum is my approach.
So: Is the power warning light off now?
(You might need to consider that you have two separate problems).
If some vakuum suction on the brake booster is observed, let's assume the vakuum is OK.
Now for the brakes:
With vakuum disconnected or engine off: How does the pedal feel?
Probably still hard.
First: I suggest to remove the brake pads on the front and verify the calliper pistons are not seized.
Second:
Your master brake cylinder might have failed and fluid might have seeped behind the piston, obstructing it to move. Might be hard to tell whether break pressure is build up, preventing further movement, or something is seized.
I suggest to setup for bleeding brakes: a hose from bleeding nipple into a container with brake fluid / no air in this. Open the bleeder and check the pedal. As the brake circuit is open now, there should be almost no resistance to move the pedal, and you should observe brake fluid to be moved.
If there is still a hard pedal: Something is seized. Diagnose the actuation linkage and the master cylinder then.
With no vakuum applied, the brake booster should just pass on the pedal linkage to the master cylinder. Disconnect master cylinder from brake booster and check movement of the components individually.
Even without boost, the brakes are supposed to operate and the pedal must move.
I think, it's the master cylinder.
Good Luck Ralf
