* Under the hood in the fuse box: This is the most common location. The fuse box is usually located near the battery, often under the hood. Look inside the fuse box for a relay labeled "fuel pump," "EFI," or something similar. The relay itself might be a standard automotive relay (you can often identify it by size and shape).
* Under the dash fuse panel: Less common, but possible on some models. Check your owner's manual if you have it for the most accurate diagram and locations of your specific fuses and relays.
* Behind the glove box: Another less common spot, but worth checking if you don't find it in the other locations.
To find it definitively:
1. Consult your owner's manual: This is the best resource. It will have a diagram showing the location of all fuses and relays.
2. Use a wiring diagram: A wiring diagram specific to your 1991 F-150's engine and options will pinpoint the relay's location and its circuit. These are often available online through automotive repair sites or forums.
3. Look for a relay that matches the description: Even without a diagram, look for a relay that is in a common relay location (fuse box under the hood, or under the dash) that matches the description for a fuel pump relay. It's typically a fairly standard-looking component.
Important Note: Before working on any electrical components, disconnect the negative battery terminal to prevent accidental short circuits.
