mtncat

I have a 1990 F150 4x4 w/ 5.0 and 5 speed. Something is wrong with the fuel pumps (dual Tanks). Neither of them come on when key is turned to run position. No power at either pump. I am thinking it is the inertia switch or the fuel pump relay, but I cannot locate either of these pieces. Chilton book says inertia switch is under right side of dash, very nonspecific and unhelpful. Nothing is said of the location of fuel pump relay. Any help is appreciated.

ModMech

Inertia switch is on the right side, against the kick panel just infront of the door opening, at the level of the top of the plastic kick panel. Small shit button.

The fuel pump relay is either in the underhood relay box, or bolted to the front sheet metal near the left headlamp (I'm not sure which on a '90).

Another VERY common cause is corroded terminals at the harness connectors (under the master cylinder, and under driver's seat on innside of frame rail).

fuelman

I would change the fuel tank selector switch in the dash. This switch will arc the contactors inside killing power to both pumps.