I assume its not the original charging system?
Alternator with Internal volatge regulator?
And master cylinder?
The alternator will have a Light Green wire for the Voltage regulator
That wire comes from the ignition switch, it has 12volts with key on, this wire would PASS THRU a 12volt light bulb in the dash, you would also have a 550 ohms resistor between both terminals on the bulb, this is a backup in case bulb should burn out
When you turn on the key the alternator is a Ground, 0volts, so "Battery Light" has 12v on one terminal and 0 Volts on the other, so it LIGHTS UP.
When you start the engine, and if alternator is working, lol, the Battery Light now has 12volts on BOTH terminals, so it goes OFF
It actually should have 14volts on both, but you get the idea.
This setup is the ON/OFF for the alternator, if voltage regulator is given 12volts all the time it will run down the battery.
So the Green wire should only have Key on 12volts, this is also the Start Up voltage the alternator needs to start "making" its own voltage, so if the light bulb should burn out then no alternator, which is why you need the resistor, but up to you
Resistor is no "required" for the circuit to work, its a safety back up so alternator can always charge battery
The Brake warning light gets 12volts with key on
Then it has 2 possible grounds, the Fluid level in master, or the Parking Brake pedal switch
So on the master one terminal goes to a ground, the other to the Bulb, when fluid is low switch closes and bulb lights up
These 12volt key on sources need to be Fused, they could share the same fuse, 10amp would be more than enough, 7.5amp would do