To find it, you need to specify the make and model (e.g., "1994 Ford F-150," "1994 Chevrolet Silverado," "1994 Toyota Tacoma"). Once you provide that information, a more precise answer can be given.
Generally, it's located somewhere in the area of the transmission bellhousing, near where the clutch fork is. It might be on the top, the side, or even the bottom, depending on the vehicle's design. A repair manual specific to your truck's year, make, and model will be the most reliable resource for its exact location.