There isn't a readily accessible, dedicated fuel pump kill switch installed in a 1989 Ford Aerostar from the factory. The fuel pump is controlled electrically through the ignition system and various safety interlocks. Disconnecting the power to the fuel pump requires accessing the wiring harness, typically near the fuel pump itself (under the vehicle) or at the engine control module (ECM). This is not a simple task and requires some mechanical knowledge.
Caution: Improperly disconnecting or tampering with the fuel pump wiring could lead to damage to the vehicle's electrical system or even create a fire hazard.
If you need to disable the fuel pump for safety or other reasons, consider professional help from a qualified mechanic rather than attempting to install a kill switch yourself. They can safely locate and disconnect the appropriate wire or install a proper after-market switch.
