1984 Nissan 300ZX Heater, brake lights

With reference to the brake lights, check the brake light switch, it is mounted on the pedal itself. With reference to the heater. There are two rubber lines that go into the fire wall. Check to see if they get warm or hot. If not then there could be a couple of things, first the thermastat otr the heater core is clogged. If the heater core is blocked you may be able to back flush the core without taking it off the car. They have back flush kits available at most auto stores.