Location 1: Under the Hood, in the Power Distribution Box (PDB):
* Finding it: Open your hood. The Power Distribution Box is usually a large black plastic box near the battery, often attached to the inner fender wall. It has many fuses and relays. The fuel pump relay is usually within this box. The box itself often has a diagram on its lid or inside the lid showing the relay positions. This diagram is crucial.
* Identifying it: Unfortunately, there isn't a universally marked "Fuel Pump Relay." You'll likely need to consult a wiring diagram specific to your 1991 Mustang LX 2.3L (see below on how to obtain one). The diagram will show which relay controls the fuel pump. It might be labelled with a number or a vague description like "Engine Control Relay" or something similar—the diagram is essential for certainty.
* Replacing it: Once identified, simply pull the relay straight out of its socket. Push the new relay in, ensuring it's correctly oriented (there's usually a small tab to guide it).
Location 2 (Less Common): In the Passenger Compartment Fuse Box:
* Finding it: This is less common for the fuel pump relay on this model year but possible. Locate the fuse box inside the passenger compartment (usually under the dashboard).
* Identifying and Replacing: Similar to above, you'll need the wiring diagram to locate the correct relay and replace it.
How to Find the Correct Wiring Diagram:
A wiring diagram is *absolutely essential* for accurate identification of the fuel pump relay. Here are some ways to obtain one:
* Online Resources: Websites specializing in automotive repair manuals (like Haynes or Chilton) often sell downloadable PDFs of wiring diagrams. Make sure you specify the year, model, and engine size (1991 Ford Mustang LX 2.3L).
* Ford Dealer: Your local Ford dealership's parts department might be able to provide a wiring diagram, although it might come at a cost.
* Auto Parts Stores: Some larger auto parts stores may have access to wiring diagrams or repair manuals on their computers.
Important Note: Before you start, disconnect the negative terminal of your battery to prevent accidental short circuits. Also, make sure you get the correct replacement relay—the wrong relay could cause further problems. The relay should be specifically rated for the amperage required by the fuel pump.
Remember, safety first! If you're not comfortable working with automotive electrical systems, it's best to take your Mustang to a qualified mechanic.
