The modulator valve is located on the transmission case, usually on the passenger side (right side as you sit in the car). It's a small fitting, often with a vacuum hose already attached to it – this is where you connect your modulator hose.
The other end of the modulator hose attaches to a vacuum source on the engine, often near the intake manifold. The exact location varies depending on the specific engine setup and year, but it will be a vacuum port. Look for a small vacuum port with a hose already attached, or consult a shop manual or wiring diagram for your specific 1984 454 Chevy to be certain.
