Power To Fuel Pump Check (1997-2010 4.6L, 5.4L V8 Ford F150, F250, And F350)

When troubleshooting an engine no-start —and you've confirmed the fuel pump isn't producing any pressure (like with a fuel pressure test gauge)— it's important to make sure the fuel pump is actually getting power.

The really cool thing about Fords is that checking power to the fuel pump is pretty easy, thanks to the fuel pump inertia switch.

Since the inertia switch is so easy to access, checking for power there is a piece of cake —and it'll quickly tell you if the fuel pump fuse and relay are doing their job.

In this tutorial, I'll show you step by step how to make sure the fuel pump is getting the power it needs to run —so you can confidently confirm that the zero PSI reading you got on your gauge is legit, and not caused by a power issue.

NOTE: This info mainly applies to non-FPDM (fuel pump driver module) F-Series pickups —but the power-in and power-out tests at the fuel pump inertia switch still apply to all models, whether they use an FPDM or not.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.6L V8 Ford F150: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008.
• 5.4L V8 Ford F150: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008.
• 4.6L V8 Ford F250: 1998, 1999.
• 5.4L V8 Ford F250: 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 5.4L V8 Ford F350: 1999, 2000, 2001, 2002, 2003, 2004, 2004, 2005, 2006, 2007, 2008, 2009, 2010.

NO-START DIAGNOSTICS: If you're troubleshooting a no-start or fuel pump issue, be sure to check out the list of wiring diagrams, fuel pump tests, and related diagnostics at the bottom of this page:

• More Fuel Pump Troubleshooting Help.

It'll help you dig even deeper if the inertia switch isn't the problem.

Why You Should Check For Power Before Replacing The Fuel Pump

Whenever you get a 0 PSI fuel pressure reading from your fuel pressure gauge, the next logical step is to make sure the fuel pump is getting power.

On 1997–2004 F-Series pickups that do not use a fuel pump driver module (FPDM), power is delivered directly to the fuel pump when you turn the key and crank the engine —no FPDM module in between.

To be more specific, during cranking, voltage flows from the fuel pump fuse → to the fuel pump relay → then to the fuel pump inertia switch. If the switch hasn't been tripped, it passes that power straight to the pump.

The whole point of this test is to rule out a blown fuse or a bad relay that could be stopping the fuel pump from getting power and running.

On F-Series pickups, this test is a piece of cake —you just access the fuel pump inertia switch's 2-wire (or 3-wire) connector and check for power there.

If power is present at the inertia switch's connector, we now know the fuel pump fuse and relay are doing their job —and we can now confidently drop the tank and replace the pump.

Before we get into the step-by-step, let's go over the few tools you'll need to perform the test.

What Tools You'll Need

You won't need a scan tool or any other expensive diagnostic equipment for this test, just a few simple tools:

• Test light or multimeter: Either one gets the job done. You'll be checking for battery voltage at the fuel pump inertia switch. If you don't already own one, these are the ones I own and use myself:
  • Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).
  • Lisle 28400 Heavy Duty 12 Volt Test Light (Amazon affiliate link).
• Access to the inertia switch: You'll usually find it tucked behind the passenger-side kick panel, just below the glove box.
• Someone to crank the engine: You'll need a helper to turn the ignition and crank the engine while you probe for voltage at the connector.

Disclosure: As an Amazon Associate, I earn from qualifying purchases. Buying through these links helps support this site at no extra cost to you. Thanks for your support —it really means a lot!

How To Check That Power Is Reaching The Fuel Pump (Via The Inertia Switch)

Alright, let's get down to business. To find out if the fuel pump is actually getting the voltage it needs to run, we're gonna check the power-in wire and the power-out wire at the fuel pump inertia switch.

NOTE: This test applies to both non-FPDM and FPDM-equipped F-Series pickups. On models with an FPDM, the inertia switch wiring is the same —the only difference is that the switch sends power to the FPDM, not directly to the fuel pump.

PART 1: Step-By-Step Power-In Test:

1. Locate the inertia switch: You'll find it behind the passenger-side kick panel, right under the glove box. Pop off the plastic trim to get to it —you'll see a 2-wire or 3-wire electrical connector plugged into the switch.
2. Unplug the connector: You'll see two or three wires going to the switch. One of them brings power in from the fuel pump relay. The other one sends power out to the pump. To ID the power-in wire, see:
   • Fuel Pump Inertia Switch Circuit Descriptions.
3. Crank the engine: Have a helper crank the engine while you test the power-in wire with your test light or multimeter.
4. Check for 10 to 12 Volts DC: If you see battery voltage (or close to it) on the power-in wire during cranking, that's a good sign. That means the fuel pump fuse, the fuel pump relay, and all the wiring up to this point are working.
5. No voltage? Then you've just ruled out the pump as the cause of the no-start. The problem is upstream: blown fuse or a bad fuel pump relay —or maybe the PCM isn't grounding the relay. That's gonna be the focus of your troubleshooting efforts from this point.
6. Voltage is present? Good —that means the inertia switch is getting power. But now we need to make sure it's actually passing that power along to the fuel pump.

PART 2: Step-By-Step Power-Out Test:

1. Reconnect the connector: Go ahead and plug the 2-wire (or 3-wire) connector back into the inertia switch so we can test the power-out side with everything connected.
2. Backprobe the power-out wire: With your multimeter's red lead, backprobe the power-out wire —the one that feeds voltage directly to the fuel pump. If you're not sure which wire is which, see:
   • Fuel Pump Inertia Switch Circuit Descriptions.
3. Ground your black lead: Touch the black lead to clean, bare metal close to the inertia switch. No paint. No rust. You need a solid Ground for an accurate reading.
4. Crank the engine: Have your helper crank the engine again while you watch the multimeter display.
5. Read the voltage: If the inertia switch is working like it should, you'll see 10 to 12 Volts on the power-out wire during cranking. That means it's passing power through to the pump —and if you've still got 0 PSI on the gauge, you've just confirmed a dead pump or a seriously blocked fuel line (which is rare).

IMPORTANT: This test doesn't tell you if the pump is producing pressure —it only confirms that it's getting voltage. But it's an important step to take before dropping the tank and swapping the pump.

Fuel Pump Inertia Switch Circuit Descriptions

Below you'll find the wire color info for both terminals of the fuel pump inertia switch connector —organized by model year so you know which wire to test for power in and power out.

NOTE: Fuel Pump Driver Module (FPDM) equipped vehicles:

• F150: 2004-2010.
• F250: 2005-2010.
• F350: 2005-2010.

More Fuel Pump Troubleshooting Help

FUEL PUMP PRESSURE TESTS:

• How To Test The Fuel Pump (1997-2004 4.6L, 5.4L V8 Ford F150, F250, And F350).

FUEL PUMP PRESSURE SPECIFICATIONS:

• Fuel Pressure Specifications (1997-2010 4.6L, 5.4L V8 Ford F150, F250, And F350).

INERTIA SWITCH (FUEL PUMP) CIRCUIT DIAGRAMS:

• Fuel Pump Circuit Wiring Diagram (1997-1998 4.6L, 5.4L V8 Ford F150, F250 Light Duty).
• Fuel Pump Circuit Wiring Diagram (1999 4.6L, 5.4L V8 Ford F150, F250 Light Duty).
• Fuel Pump Circuit Wiring Diagram (2000-2003 4.6L, 5.4L V8 Ford F150 Pickup).
• Fuel Pump Circuit Wiring Diagram (2000-2004 5.4L V8 Ford F250 And F350 Pickup).

More 4.6L, 5.4L V8 Ford F150, F250, And F350 Diagnostic Tutorials

You can find a complete list of tutorials and wiring diagrams in this index:

• 4.6L, 5.4L Ford F150, F250, And F350 Index of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Throttle Position Sensor (1997-2004 4.6L, 5.4L Ford F150, F250).
• How To Test The Coil-On-Plug Ignition Coils (1997-2010 4.6L, 5.4L Ford F150, F250, F350).
• How To Test The Fuel Injectors (1997-2002 4.6L Ford F150, F250).
• How To Test The Alternator (1997-2003 4.6L, 5.4L Ford F150, F250 Light Duty).