The 7.3L Powerstroke utilizes injector harnesses which live under the valve cover (UVCH). These harnesses live their whole lives in a very harsh environment. They exist in a constant hot oil bath. These harnesses are detrimental to a well running 7.3 and any issues with them will cause running issues. Make sure you're using only the best when replacing them. Copy-cat products are everywhere. Here at Riffraff Diesel we pride ourselves in only offering the best products available. Which is why we stock genuine Motorcraft Under Valve Cover Harnesses. 

Note:

For 1999-2003 Super Duty trucks, you'll need to order one per side. So two total if you're doing both heads.

1999-2003 Under Valve Cover Harness (Ford PN F81Z9D930AB):  https://www.riffraffdiesel.com/under-valve-cover-harness-99-03/

For 1994.5-1997 OBS trucks, you'll need two per side. So four total if you're doing both heads.

1994.5-1997 Under Valve Cover Harness (Ford PN F4TZ9D930K):  https://www.riffraffdiesel.com/under-valve-cover-harness-94-5-97/