If the connector has been hot or melted work on that end first.
Check for 12 volt power at gray wire on the wiring plug for fuel pump power engine run or key on engine prime.
Also make sure you are getting ground on black wire.
If you have a 1999 350 engine code R it also has a balance fuel pump and relay and balance module on left fram rail.
All of that has to work right for the in tank fuel pump to run.
Also do you have dual tanks.
Any check engine lights or codes?
Before you get very deep in the fuel pump/balance pump and balance pump module and relay or fuel system on it.
I would suggest you get all data DIY sub for it.
http://www.alldata.com/products/diy/index.html
MT