To be certain, it's best to:
* Check your owner's manual: This is the definitive source.
* Look carefully around the dashboard: Pay close attention to areas near the radio, heater controls, and other switches. It might be a small, somewhat inconspicuous switch.
* Consult a Ford F-150 parts diagram online: This can show you a visual representation of the dashboard layout.
If you can't find it, a local Ford mechanic or parts specialist familiar with 1984 models should be able to quickly point out the switch's location.