03 Mustang Fuel Pump Relay Location: Complete Guide to Finding and Replacing It

The bottom line: On a 2003 Ford Mustang GT, the fuel pump relay is not in the standard fuse box. It is located inside the Constant Control Relay Module (CCRM), which is mounted inside the passenger side front fender, behind the inner fender liner. For 1996-2004 Mustangs, you’ll need to remove the inner fender liner on the passenger side to access the CCRM, where the fuel pump relay is housed alongside several other relays . If you’re driving a V6 model, the location is generally the same. This is a common point of confusion, and many owners waste time searching under the dash or in the trunk — don’t make that mistake.

Why the Fuel Pump Relay Matters

The fuel pump relay is a small electrical switch that controls power to the fuel pump. When you turn the key to the "ON" position, the relay closes for about 2-3 seconds, sending power to the pump so it can pressurize the fuel system before you start the engine . If the relay fails, the fuel pump won’t receive power, and your engine will crank but won’t start .

On a 2003 Mustang, a failing relay can cause symptoms that are almost identical to a dead fuel pump:

  • Engine cranks but won’t start. You turn the key, the starter spins, but the engine never fires up.
  • No fuel pump prime sound. With the key in the "ON" position, you should hear a brief humming noise from the rear of the car (the fuel tank). If you don’t hear it, the relay or the pump itself may be at fault.
  • Intermittent stalling or hard starting. If the relay is failing internally, it may work sometimes and fail others, leading to random no-start conditions .

Step 1: Locate the Fuel Pump Relay on Your 2003 Mustang

The most important thing to know is that the fuel pump relay on a 2003 Mustang is not in the main fuse box under the hood. It is part of the CCRM, which stands for Constant Control Relay Module. This module is a black box that contains multiple relays for the fuel pump, cooling fan, A/C compressor, and other systems .

Here’s exactly where to find it:

  1. Open the passenger side front door. You’ll be working on the passenger side fender area.
  2. Remove the inner fender liner. This is the plastic panel inside the wheel well. You may need to remove a few screws or push pins to pull it back. On some models, you can access it by just pulling back the liner without fully removing it.
  3. Look for the CCRM. It is mounted to the inner fender structure, near the front of the passenger footwell area. It’s a rectangular black box, about the size of a paperback book, with multiple wires and connectors going into it.
  4. The fuel pump relay is inside the CCRM. You cannot simply pull out a single relay like you would from a fuse box. The CCRM is a sealed module. In most cases, you will need to replace the entire CCRM if the fuel pump relay is bad, or you can carefully open the CCRM and replace just the relay if you’re comfortable with soldering.

For 2003 Mustang GT owners specifically: The CCRM is located behind the passenger side front fender, and you must remove the inner fender liner to see it . This is different from many other Ford vehicles where the relay is in the main fuse box.

Step 2: Diagnose a Bad Fuel Pump Relay Before Replacing It

Before you go through the hassle of accessing the CCRM, it’s wise to confirm that the relay is actually the problem. A failed relay is far more common than a failed fuel pump motor, and it costs significantly less to fix .

Here’s a simple test you can do:

  1. Listen for the pump. Turn the key to the "ON" position (don’t start the engine). Listen near the rear of the car — you should hear a faint humming sound from the fuel tank for about 2 seconds. If you hear it, the relay is likely working, and the problem is elsewhere .
  2. Check the fuel pump fuse. While you’re at it, open the main fuse box under the hood (the one near the battery) and check the fuel pump fuse. A blown fuse is a $1 fix that can cause the exact same symptoms as a bad relay .
  3. Check the inertia switch. The 2003 Mustang has an inertia fuel shutoff switch, typically located in the passenger footwell or in the trunk. If this switch has been tripped (from a bump or impact), it cuts power to the fuel pump. Press the reset button to see if your car starts .

If you’ve ruled out the fuse and the inertia switch, and you still don’t hear the pump prime, the relay or the pump itself is the likely culprit.

Step 3: Replace the Fuel Pump Relay

Replacing the fuel pump relay on a 2003 Mustang is a bit more involved than on most cars because you have to deal with the CCRM. Here’s the step-by-step:

  1. Disconnect the battery. Always disconnect the negative battery cable before working on any electrical components. This prevents accidental shorts and keeps you safe .
  2. Access the CCRM. As described above, remove the passenger side inner fender liner to expose the CCRM.
  3. Remove the CCRM. Unbolt or unclip the module from its mounting bracket. Disconnect the electrical connectors. Be careful not to damage the wiring.
  4. Open the CCRM. The module is usually sealed with epoxy or plastic clips. You may need to carefully pry it open. Some aftermarket replacements are available as a complete unit, which is often easier.
  5. Replace the relay. Inside the CCRM, you’ll see several small relays. The fuel pump relay is usually labeled on the circuit board. If you can solder, you can desolder the old relay and solder in a new one. If not, buy a new CCRM as a complete unit.
  6. Reinstall everything. Mount the new (or repaired) CCRM back in place, reconnect the wiring, and reinstall the inner fender liner. Reconnect the battery.

Tip: If you’re not comfortable with soldering or opening the CCRM, the simplest fix is to buy a new CCRM from an auto parts store or online. They are readily available for 1996-2004 Mustangs and cost between $50 and $150, depending on the brand.

Step 4: Test Your Work

After you’ve replaced the relay or the CCRM, test the system:

  1. Reconnect the battery. Make sure the negative terminal is tight.
  2. Turn the key to the "ON" position. Listen for the fuel pump to prime for 2-3 seconds. If you hear the hum, the relay is working.
  3. Start the engine. If the car starts and idles smoothly, you’ve fixed the problem. If it still doesn’t start, the issue may be with the fuel pump itself, the wiring, or the fuel filter .

Common Mistakes to Avoid

  • Don’t assume the relay is in the fuse box. On a 2003 Mustang, the fuel pump relay is not in the main fuse box. Searching there will waste your time .
  • Don’t replace the fuel pump before checking the relay. A bad relay can mimic a dead fuel pump perfectly. Swapping the relay (or the CCRM) is a cheap and easy first step. Replacing the fuel pump is a much bigger job that requires dropping the tank or cutting an access hole .
  • Don’t forget the inertia switch. Make sure the switch hasn’t been tripped. It’s a common oversight that leads to unnecessary repairs .

Why You Should Consider a High-Quality Fuel Pump Replacement

If you’ve confirmed that the fuel pump itself is the problem — not the relay, fuse, or inertia switch — you’ll need a reliable replacement. The fuel pump is the heart of your fuel system, and a cheap pump can fail in a matter of months, leaving you stranded.

KEMSO Racing offers high-performance, OEM replacement fuel pumps that are built to last. Their pumps are designed to meet or exceed factory specifications, ensuring a perfect fit and reliable performance. Here’s why KEMSO stands out:

  • High Performance: KEMSO fuel pumps are engineered for maximum flow and pressure, ensuring your engine gets the fuel it needs under all driving conditions.
  • OEM Replacement: They are direct replacements for your original pump, meaning no modifications or extra parts are needed. Just install and go.
  • Lifetime Warranty: Every KEMSO fuel pump comes with a lifetime warranty. This means if it ever fails, you get a replacement at no cost. That’s peace of mind you don’t get with cheap store-brand pumps.

To learn more about the right fuel pump for your 2003 Mustang, visit KEMSO Racing today:

https://www.kemsoracing.com/

Final Thoughts

Finding the fuel pump relay on a 2003 Mustang is not as straightforward as on most cars, but once you know it’s in the CCRM behind the passenger fender, the job becomes much easier. Start with the simple checks — the fuse and the inertia switch — before diving into the relay replacement. If you do need to replace the relay, you have the option of repairing the CCRM or replacing it entirely. And if the fuel pump itself is the culprit, a quality replacement like those from KEMSO Racing will keep your Mustang running strong for years to come.

For more information on high-quality fuel pumps and other automotive parts, be sure to check out KEMSO Racing at https://www.kemsoracing.com/.


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