I have a Lincoln Continental 2000 and had changed the fuel pump one time and it worked for about a month and after a month the fuel pump failed again and confirmed it failed by applying 12v and ground to the fuel pump motor with a car battery. After that I bought another fuel pump and changed it and I noticed that the connector has 12v and ground but as soon as I connect it to the new fuel pump, it loses 12v, I checked with the multimeter on the fuel pump motor. I checked with other fuel pump motors that I have, not knowing if they work or not and it does the same thing, 12v disappear. When fuel pump connector is disconnected, there is 12v. I have changed the FPDM and the ECM as well to see if it would make a difference and it did not. I think this could be a wiring or a fuse box issue, since I already changed ECM and FPDM. Although I am not sure, does anybody why this is happening?
You must have a bad connection somewhere in the wiring with a high resistance, rather than a completely broken circuit that you would get from a blown fuse.
With no load connected (the fuel pump), the high resistance would allow you to see 12v at the fuel pump connector. Since a very small current is being drawn by the voltmeter, there will be no significant voltage drop (ohms law).
Once you connect the fuel pump, the fuel pump's low resistance will attempt to draw a larger current. This will then cause a large voltage drop across the high resistance bad connection.
I would start by probing the fuse for the fuel pump to see what voltage is present there while the fuel pump is powered up. If you see 12 volts there, then you know that the bad connection is after the fuse. If it is a low voltage at the fuse, the issue is before the fuse.