Fuel pump issues

[shelby racer]

Hey gang,
I need more advice / guidance. I have always had problems with the fuel pumps with csx4788. I run them all the time because no one told me that one of the fuel lines was for a mechanical fuel pump (which made it very interesting the first time I turned the fuel pumps on and had 1 psi) and had to re-ground the front one because it would not run all the time with the ground that it had. Months ago (maybe even last fall) I was running the car and the fuel pump fuse blew. I replaced the fuse and the car fired right up but I think I had shorted one of the pumps because I discovered later that it did not work anymore. I replaced it (the front pump that had been re-grounded) with a new Facet pump and everything was happy. Last Thursday night I blew the fuel pump fuse again (which is why I wrote the forum last week) but this time, as soon as I replaced the fuse , it blew again. I have been doing diagnostics today and I get 12 - 14 v at the fuse box and at the power connections at the pumps. When I give power to only the new pump, it is happy. When I give power to the old pump (or both pumps) the fuse immediately blows. Should I just replace the old pump? Are the pumps not meant to be run all the time (even though they are sold as race pumps to be used as the sole source of fuel)? Are there any other tests to try and determine why the pump went bad / is shorting the circuit? Any help or insight is appreciated. Thanks.
John(;-)