I have an 88 240 ever since I took ownership of it 2 years ago the brake light failure light has remained on ive changed the rotors and pads front and rear and the mc with booster what will make it turn off the brakes are perfect

 

There is a brake proportion valve in the system which is a safety feature that will shut off some brakes in the circuit if you have a brake line failure. It is a small block on the firewall that has multiple brake lines going into it. There is a switch with a single wire in it. If you unplug the wire the light should go out. If it does then the switch is bad or the valve is bad.

 

thank you ill try that in the morning I appreciate it I'm super new to Volvo ownership

 

the switch doesn't shut off brake circuits... it warns you if the pressure is unequal between the circuits, which is an indication something is wrong.

one circuit is half of each of the front brakes, and one rear brake, the other circuit is the other half of both front brakes, and the other rear.

its possible a slave cylinder is bad, its possible the switch itself is bad, its possible the wire is shorted to ground somewhere.