To effectively stop fuel flow, you would need to:
* Disconnect the negative battery cable: This is the safest and most reliable way to completely shut down electrical power to the fuel pump.
* Locate and disconnect the fuel pump relay: This is usually in the underhood fuse box. This will stop power to the fuel pump without completely killing the entire vehicle's electrical system. You'll need a wiring diagram or the owner's manual to identify this relay.
There's no easily accessible switch designed for this purpose on the 1988 Bronco. Any aftermarket installation would be a custom addition.