It means the customer is probably going to kick your @zz if you don't reinstall his old fuel pump and diagnose what the real cause of the open circuit is. If it has an immobilizer system , did you try another  key? Does the scanner show rpm when cranking. Does pump have a good ground you can reliably put a load on? Are you sure your test light had a good ground back there when you were testing for power at the fuel pump connector , or when either activating pump with your scan tool, or for a second or two when an assistant cycles the ignition key from off to on , or when cranking?

 If it has a TIPM for the engine compartment fuse/relay box maybe this might be helpful, in fact the Bypass kit probably could be used to bypass even other circuits of a bad TIPM.

https://www.youtube.com/watch?v=PbOae77t-wU