1988 F150 fuel pump
I have a 88 F-150 with a 351w and had the same problem just a couple weeks ago. Got to looking at the main fuel pump along the left rail and when I would wiggle the red wire I would hear the pump come on. To make a long story short I took the pump off and flattened the red spade on the wire, put it back on and haven't had any trouble since.