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It sounds like you have what is a common problem with the 7.3l, the connector for the glow plugs and injectors under the valve cover has come apart, ford has a small clip that you install in the connector to prevent this from happening again, to install this clip you need to remove the valve cover. Here is a link to a page that sells them.http://puredieselpower.com/ford/99-03-ford-7.3l-powerstroke-updated-uvc-under-valve-cover-harness-clips.html
Hope this helps, let me know if you need more help.