To be absolutely sure, you'll need to:
1. Consult your owner's manual: This is the best resource for the specific location on your truck's model.
2. Use a repair manual: A Haynes or Chilton repair manual for your specific year and engine will have diagrams and detailed instructions.
3. Look online: Search for "[Your Engine Size] 1999 Dodge Ram Oil Pressure Sending Unit Location" on YouTube or a similar site. Often there are videos showing the location.
Important Note: Before working on your vehicle, always disconnect the negative battery terminal to prevent accidental shorts. Oil is hot when the engine is running, so allow ample time for it to cool down before working near the engine block.