The pump is not a likely suspect. If it shorts, which is real uncommon, it will always be shorted and will blow a fuse instantly, not after 20 minutes. Pumps usually fail when the brushes wear away and create an open circuit. Open circuits result in no current flow. Fuses blow from too much current flow.
A more common cause of too much current is a grounded wire leading from that fuse. Harnesses that slide back and forth on the body sheet metal as the engine rocks back and forth, wires draped over a sharp metal bracket, and wires that fall off their mount and onto hot exhaust parts are common causes of grounded wires. Component failure should be suspect too but things like that are hard to find when they act up so intermittently. A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.
Saturday, July 28th, 2012 AT 10:45 PM