To be certain, you should:
1. Consult your owner's manual: This is the best resource for your specific vehicle. The manual will have diagrams showing the location of all sensors and components.
2. Look near the oil filter: This is the most common location. It's a small sensor, often with one or two wires connected.
3. Use a repair manual specific to your E150's engine: A Haynes or Chilton repair manual (or a digital equivalent) will have detailed diagrams and instructions.
4. Search online for images: A Google Images search for "1993 Ford E150 [engine size] oil pressure sending unit location" might yield helpful pictures.
Remember to carefully examine the area around the oil filter as the oil pressure sending unit is often situated close by. Be mindful of hot surfaces and potentially spilled oil.