1996 Ford F150 Owner's Manual - Page 61

RWARNING To prevent electrical shock, do not use your heater with ungrounded electrical systems or two-pronged (cheater) adapters. For best results, plug the heater in at least three hours before you start your vehicle. Using the heater for longer than three hours will not damage the engine, so you can plug it in at night to start your vehicle the following morning. NOTE: Be sure to disconnect the engine block heater before driving your vehicle. If the Engine Cranks but Does Not Start or Does Not Start After a Collision Fuel Pump Shut-off Switch If the engine cranks but does not start or does not start after a collision, the fuel pump shut-off switch may have been triggered. The shut-off switch is a device intended to stop the fuel pump when your vehicle has been involved in a substantial jolt. Once the shut-off switch is triggered, you must reset the switch by hand before you can start your vehicle. 59