First off, I would like to thank you all for your help in getting a new engine a year ago for piston slap on my 2000 F150. I now have a problem with my 1990. When I turn the key to the run position the fuel pump continually runs, instead of stopping after a second. When it does this it will not start. I know that their is a short somewhere because it does it intermittently. My problem is that I do not know what controls the length that the pump runs before starting. I have no clue where to start looking. I changed the pressure regulator and fuel pump relay. If any one knows about the wiring system please help.

 

The fuel pump should run continuously. It doesn't stop and start due to fuel demands. The noise you hear when the key is initially turned is probably the pump priming itself. When the engine isn't running, all of the fuel is returned the the tank. Your inertia switch is OK, otherwise the pump wouldn't run at all.

If you can hear it running (trying to prime itself), I suspect that either the pump is bad or the strainer that is usually located on the fuel pickup is plugged. You may also have a plugged fuel filter, I would start there first.

Good luck.