1999 Mercury Sable Fuel Pump Relay Location: A Complete DIY Guide

Here is the bottom line: On a 1999 Mercury Sable, the fuel pump relay is located in the power distribution box (under-hood fuse box) near the battery. It is specifically relay number 29, and the fuel pump itself is protected by a 20A fuse located at position number 10 in the same box.

If your 1999 Mercury Sable is cranking but not starting, or if it stalls out while driving and then refuses to restart, a bad fuel pump relay is a common and relatively easy fix. Before you tear into the fuel tank or spend money on a tow truck, checking and replacing the relay is the smart first step. This guide will walk you through exactly where to find it, how to test it, and what to do if the relay is not the problem.

Where Is the Fuel Pump Relay on a 1999 Mercury Sable?

The location varies slightly depending on the engine (3.0L V6 or 2.0L 4-cylinder) and trim level, but the most common and widely accepted location is the under-hood power distribution box.

The Primary Location: Under-Hood Power Distribution Box

  1. Open the hood. Make sure the engine is off and cool.
  2. Locate the power distribution box. This is a large black plastic box usually located near the battery on the driver's side of the engine compartment. It is sometimes called the "fuse box" or "relay box."
  3. Remove the cover. The cover typically has clips on the sides. Press them in and lift the cover off.
  4. Check the diagram on the underside of the cover. The diagram will show the layout of all fuses and relays. Look for "Fuel Pump Relay" or "FP Relay."
  5. Identify relay number 29. According to the official 1999 Mercury Sable owner's manual and fuse box diagrams, the fuel pump relay is specifically relay number 29. It is often a square or rectangular relay with multiple pins.

The Alternate Location: Passenger Compartment Fuse Box

This is less common for the 1999 Sable, but some owners have reported finding it here. If you cannot find the relay under the hood, check the interior fuse panel. It is located below and to the left of the steering wheel, near the brake pedal. Again, look for the diagram on the fuse box cover.

How to Test the Fuel Pump Relay

Before you buy a new relay, it is smart to test the existing one. Here is a simple, safe method that works on most cars.

The Swap Test

This is the easiest way to diagnose a bad relay without a multimeter.

  1. Locate the fuel pump relay (relay 29).
  2. Find an identical relay in the same box. Look for a relay that has the same shape, size, and number of pins. Common non-critical relays to swap with include the horn relay, the A/C clutch relay, or the blower motor relay.
  3. Swap the relays. Pull out the fuel pump relay and the relay you chose to swap. Plug the known-good relay (e.g., the horn relay) into the fuel pump relay slot.
  4. Try to start the car. If the engine starts and runs normally, the fuel pump relay was faulty. You have found the problem. Replace it with a new relay of the same type.
  5. If the car still does not start, the problem is likely not the relay. It could be a faulty fuel pump, a bad fuel pump fuse, a clogged fuel filter, or an issue with the fuel pump inertia switch.

Using a Multimeter (Optional)

If you have a multimeter, you can test the relay directly.

  1. Set the multimeter to measure resistance (ohms).
  2. Identify the relay's pins. Most relays have four pins: 85, 86, 87, and 30. Pins 85 and 86 are the control circuit (coil). Pins 30 and 87 are the power circuit (switch).
  3. Test the coil. Place the multimeter probes on pins 85 and 86. You should see a resistance reading, typically between 50 and 200 ohms. If you see infinite resistance (OL), the coil is open and the relay is bad.
  4. Test the switch. Place the probes on pins 30 and 87. You should see infinite resistance (open circuit). Now, apply 12V power to pin 85 and ground pin 86 (you can use a battery and jumper wires). You should hear a click, and the multimeter should now show near-zero resistance (closed circuit). If it does not click or the circuit does not close, the relay is bad.

What If the Relay Is Good? Other Common Causes of a No-Start

If you have tested the relay and it works, or if swapping it did not help, you need to look at other parts of the fuel delivery system.

1. Check the Fuel Pump Fuse

The fuel pump is protected by a 20A fuse located in the same power distribution box as the relay. It is fuse number 10. Pull the fuse and inspect the metal strip inside. If it is broken, the fuse is blown. Replace it with a new 20A fuse of the same type. If the new fuse blows immediately, you have a short circuit in the fuel pump wiring or the pump itself.

2. Inspect the Fuel Pump Inertia Switch

The 1999 Mercury Sable has a fuel pump inertia switch (also called a fuel shut-off switch). This switch is designed to cut power to the fuel pump in the event of a collision. It can also trip from a hard bump or pothole.

  • Sedan models: The switch is located on the right side of the trunk, behind the trunk liner.
  • Wagon models: The switch is located behind the service panel on the right side of the cargo area.

To reset it, press the button on top of the switch. It should click. Try starting the car again.

3. Listen for the Fuel Pump

When you turn the ignition key to the "ON" position (without cranking the engine), you should hear a faint whirring noise from the fuel tank for about 2-3 seconds. This is the fuel pump priming. If you do not hear it, the pump may be dead.

4. Check for Power at the Fuel Pump

If you have a multimeter, you can check for power at the fuel pump connector. This is located on top of the fuel tank. You will need to access the pump through an access panel in the trunk or under the rear seat. With the ignition on, there should be battery voltage at the pump connector for a few seconds. If there is no power, the problem is in the wiring, relay, or fuse.

How to Replace the Fuel Pump Relay

Replacing the relay is a straightforward task.

  1. Disconnect the negative battery terminal. This is a critical safety step to prevent accidental shorts and electrical shocks.
  2. Locate the bad relay (relay 29).
  3. Pull the relay straight out. You may need to wiggle it gently. Do not pry it with a screwdriver, as you can damage the relay socket.
  4. Insert the new relay. Make sure it is oriented the same way as the old one. Push it down firmly until it clicks into place.
  5. Reconnect the negative battery terminal.
  6. Test the system. Turn the key to the "ON" position and listen for the fuel pump to prime. Then try to start the engine.

Why You Should Trust the Power Distribution Box Location

The information from the official 1999 Mercury Sable owner's manual and multiple automotive repair websites consistently points to the under-hood power distribution box as the correct location for the fuel pump relay. The manual specifically identifies relay number 29 for the fuel pump. This is the most reliable and authoritative source. Using the owner's manual is always the best starting point for any repair on your specific vehicle.

When to Call a Professional

If you have checked the relay, the fuse, the inertia switch, and you are still not getting fuel to the engine, the problem may be more complex. It could be a faulty fuel pump itself, a wiring issue, or a problem with the Powertrain Control Module (PCM). At this point, it is a good idea to consult a qualified mechanic. They have specialized diagnostic tools, such as a fuel pressure gauge and a scan tool, to pinpoint the exact cause of the problem.

Recommended Fuel Pump: KEMSO

If you have determined that the fuel pump itself is the issue and needs to be replaced, you need a reliable, high-quality replacement part. We recommend the KEMSO brand for your 1999 Mercury Sable. KEMSO fuel pumps are designed as high-performance, OEM replacement units. They are built to meet or exceed the original equipment specifications, ensuring a perfect fit and reliable operation. Best of all, every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind long after the installation is complete. Whether you are a DIY mechanic or a professional shop, KEMSO provides the quality and durability you need.

To browse the full selection of KEMSO fuel pumps for your vehicle, visit their website at: https://www.kemsoracing.com/

Summary

Finding and replacing the fuel pump relay on a 1999 Mercury Sable is a simple DIY task that can save you a lot of time and money. The relay is located in the under-hood power distribution box (near the battery) and is identified as relay number 29. Always test the relay with a simple swap before buying a new one, and do not forget to check the 20A fuel pump fuse (fuse 10) and the inertia switch in the trunk. If the relay and fuse are good, the problem is likely the fuel pump itself. In that case, consider a high-quality replacement like KEMSO, which offers a lifetime warranty and OEM-level performance.

For more information on KEMSO fuel pumps, visit: https://www.kemsoracing.com/


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