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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 35822
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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F150 5.0 302 engine 1/2 ton 4x4: Turned off truck....wouldn't

Customer Question

Turned off truck....wouldn't restart fuel relay n pigtail....both test 12v ....inertia switch tests only 3 ....I jumped relay yesterday n pump came on n went thru all lines n no clogs new pigtail in n relay click from relay no power to pump.... When I jump three n 4 pins on relay just a click elsewhere under hood....I am an amateur mechanic but grasp most stuff..
.electrical end getting better of me
Submitted: 2 years ago.
Category: Ford
Customer: replied 2 years ago.
Ok tested inertia switch but some things not right .....vid I saw said I'd have three wires to inertia switch ....I only have two....when I jump it n then start ....nothing ...but if I have truck on accessory n jump it ...relay clicks but still no pump power....pigtai on inertia did test out to 12 volts as did relay
Expert:  Ron replied 2 years ago.
Hello and thank you for your question, My name is ***** ***** I will assist you today.
Power to the fuel pump is supplied by the fuel pump relay from the PCM (computer) ground switching the relay, the relay is ground when the key is turned on and then once again once the computer sees the cranking signal. Once the relay is energized , power is sent out on the brown wire to the inertia switch on the brown wire and out of the inertia switch on the pink/black wire to the pump. You should have battery voltage in and out of the inertia switch for few seconds once the key is turned on and again while cranking and with the engine running. You only have two wires on your 1989. Check the voltage on both wire while cranking the engine and post back with the results and we can work from there. I have enclosed the wiring diagram for reference as well in the link below, copy and paste the link to your browser to open it.