I’m afraid the fact that the engine is a diesel is creating some issues for you.

This document about the 2003 7.3L diesel is from Ford’s Service Site:

[url=http://www.fordservicecontent.com/ford_content/catalog/motorcraft/DOBDSM30173.pdf]http://www.fordservicecontent.com/ford_content/catalog/motorcraft/DOBDSM30173.pdf

OBD-II is required for GAS engines and since the 7.3L is a diesel, it is not required to have OBD-II.

From the Ford Document:
“If a vehicle is not required to comply with OBD-II requirements, it utilizes an OBD-I system.

OBD-I systems are used on all over 8,500 lbs. GVWR Federal truck calibrations. Federal > 8,500 lbs.

OBD-I vehicles use the same PCM, J1850 serial data communication link, J1962 Data Link Connector, and PCM software as the corresponding OBD-II vehicle. ”

While they SAY it’s the same, the OBD-I system has differences in that protocol that are keeping your reader from getting the info. Simply having a J1962 connector that will accept your ELM-327 does not mean that the vehicle is OBD-II compliant.

OBD-I was very manufacturer specific and that’s why back then you needed a different reader for each manufacturer. The OBD-II standard forced all manufacturers to use the same protocol and provide the same information in “standard” areas while allowing them to have proprietary messages of their own.

Check the engine sticker on your truck and I’ll guess it says “OBD-II Exempt” rather than “OBD-II Compliant”.