1990 Ford F250 Fuel Pump Relay Location: The Ultimate Troubleshooting Guide

The fuel pump relay in your 1990 Ford F250 is located in the engine compartment's main fuse box, typically positioned near the driver-side fender or firewall. This critical relay controls power to the fuel pump, and when faulty, it causes no-start conditions, stalling, or engine performance issues. Below, we break down exactly how to locate, test, and replace it, along with symptoms and pro tips.

Where to Find the Relay (Step-by-Step)

  1. Engine Compartment Fuse Box:

    • Open the hood and locate the black plastic fuse box near the driver-side fender or firewall.
    • Remove the cover to expose fuses and relays. The 1990 F250’s fuel pump relay is one of several square or rectangular relays clustered together


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    • Identify the relay: Look for labels like "EEC," "Fuel Pump," or "FP." If labels are missing (common in older models), check your owner’s manual for a diagram. If unavailable:
      • The fuel pump relay is typically a 30-amp relay, similar in size to the horn or starter relay.
      • Trace the wiring: Follow the fuel pump fuse (20A) to its corresponding relay


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  2. Under-Dash Fuse Panel (Less Common):

    • Earlier reports suggested relays behind the dash, but for 1990–1991 F250 models, the relay resides exclusively in the engine bay


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Signs of a Failing Fuel Pump Relay

  • Engine cranks but won’t start (no fuel pressure).
  • Sudden stalling while driving, followed by a restart after 10–30 minutes.
  • No humming sound from the fuel tank when the ignition is turned "ON" (indicates the pump isn’t priming).
  • Check Engine Light with codes related to fuel circuit issues (e.g., KOEO code 542 or 543)


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How to Test the Relay

  1. Swap Test:
    • Replace the suspected fuel pump relay with an identical one (e.g., horn relay). If the engine starts, the original relay is faulty.
  2. Multimeter Check:
    • Set to continuity mode. Test pins 30 and 87 for continuity when the relay is energized (12V applied to pins 85 and 86). No continuity = failed relay


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  3. Fuel Pressure Test:
    • Connect a gauge to the fuel rail. If pressure reads 0 PSI during ignition, the relay isn’t sending power to the pump.

Replacement Guide

  1. Disconnect the battery to prevent electrical shorts.
  2. Pull the old relay straight out (no twisting required).
  3. Install a new 30-amp relay:
    • Use OEM part numbers F5TZ-9345-A or equivalent aftermarket relays (e.g., Standard Motor Products RY-1712).
  4. Reconnect the battery and test for pump priming noise


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FAQs

Can I bypass the relay?
Temporarily, yes. Jump pins 30 and 87 in the relay socket with fused wire (15–20A). Only use this to diagnose or reach a repair shop.

Why does my new relay fail quickly?

  • Wiring shorts in the fuel pump circuit.
  • Corroded terminals in the fuse box. Clean contacts with electrical cleaner and a wire brush


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Relay vs. Fuel Pump: Which is the problem?

  • If the relay clicks but the pump doesn’t run, test pump voltage. If 12V reaches the pump, the pump is dead. If not, the relay or wiring is faulty


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Pro Tips

  • Anti-corrosion spray: Apply to relay terminals to prevent future failure.
  • Carry a spare relay: Costing under $20, it’s cheap insurance against breakdowns.
  • Check ground wires: The fuel pump circuit grounds near the tank (common rust point)

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For wiring diagrams or fuse box layouts, refer to a 1990 F250 owner’s manual or reputable sources like Ford-Trucks.com forums



. Most failures stem from aging relays—replace yours every 100K miles or sooner if symptoms appear.

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