Wiring An Electric Fuel Pump: Oil Pressure Switch Guide

Wiring an electric fuel pump to an oil pressure switch is a common practice for automotive enthusiasts. This setup ensures that the fuel pump only operates when there is sufficient oil pressure, providing a level of safety in the event of a crash or engine failure. The process involves using a relay to control the high-current fuel pump with a low-current oil pressure switch. The oil pressure switch typically has three terminals, labelled S, P, and I, which correspond to different functions in the circuit. The wiring diagram provided by the user in the forum post offers a clear illustration of how to connect the fuel pump, oil pressure switch, relay, and power source. However, there is some confusion regarding the correct wiring of the S terminal on the oil pressure switch. Some sources suggest connecting it to the “S” terminal on the starter solenoid, while others recommend linking it to the ignition cranking (start) circuit to ensure fuel pump pressure during engine cranking.

How to wire the 'S' terminal on the oil pressure switch

To wire the S terminal on the oil pressure switch, you will need to follow a few important steps.

Firstly, it is essential to understand the function of the oil pressure switch. This switch is designed to indicate a loss of engine oil pressure, ensuring the engine runs smoothly. The S terminal specifically provides power to the fuel pump during engine cranking.

Now, for the wiring process:

• Identify the 'S' terminal on your oil pressure switch. This terminal is typically labelled clearly and may be colour-coded.
• Connect the 'S' terminal on the oil pressure switch to the 'S' terminal on the starter solenoid. This connection ensures that the fuel pump receives power during the engine cranking process.
• You may also need to connect the 'P' terminal on the oil pump switch to the fuel pump relay, specifically to the '86' connector.
• The '87' terminal on the fuel pump relay should then be connected to the fuel pump itself, providing power to the pump.
• Finally, ensure that the ''85' terminal on the fuel pump relay is connected to the ground.

It is important to note that you should always refer to the specific wiring diagram provided with your oil pressure switch and vehicle instructions for the most accurate and safe guidance.

Additionally, always exercise caution when working with electrical systems and ensure that you have the necessary skills and knowledge to perform the wiring safely.

How to wire the 'P' terminal on the oil pressure switch

The 'P' terminal on the oil pressure switch is the power source for the fuel pump. This is usually labelled as '30' on the fuel pump relay.

To wire the P terminal, you will need to connect it to a power source that can supply enough amps to the fuel pump. One option is to connect it to the battery side of the starter solenoid, provided it is fused or circuit breakered. This ensures that the fuel pump receives power when the ignition is turned on.

• Identify the power source: The P terminal needs to be connected to a power source that can provide enough amps for the fuel pump. This could be the battery side of the starter solenoid or any other suitable power source.
• Connect the P terminal: Use appropriate gauge wires to connect the P terminal on the oil pressure switch to the selected power source. Ensure that all electrical connectors are securely crimped and that any areas where ground leads will be fastened are clean.
• Fuse the connection: It is important to fuse the connection between the P terminal and the power source to prevent a pump malfunction or electrical fire. Use a minimum of 14-gauge wire for this connection, as recommended by experts.
• Test the setup: Once the wiring is complete, test the setup by connecting the ground cable back to the battery and starting the vehicle. Ensure that the fuel pump receives power and functions correctly.

By following these steps, you can safely and effectively wire the P terminal on the oil pressure switch, ensuring that the fuel pump receives the power it needs to operate.

How to wire the 'I' terminal on the oil pressure switch

The 'I' terminal on the oil pressure switch is the ignition terminal. This is where you will connect the ignition wire from the American Auto Wire, or the 'Tan Wire'.

The exact wiring of the oil pressure switch will depend on the type of switch you have. A typical three-wire switch will have one terminal that connects to the idiot light. This means that with no oil pressure, the terminal will be grounded, and the idiot light will be on. With oil pressure, the terminal will not be grounded, and the light will be off. The other two terminals will make a connection with oil pressure, so they will run the fuel pump.

If you have a two-wire switch, one wire will be for the idiot light, and the other will be for the ground. When there is no oil pressure, the wire will be grounded, and the idiot light will be on. When there is oil pressure, the wire will not be grounded, and the light will be off.

It is important to consult the wiring diagram that comes with your oil pressure switch, as there are different types of switches and variations in wiring.

• Power the fuel pump straight from the fuse box via a relay and inline fuse.
• Connect the oil pressure switch to the relay activation line.
• Use a switched 12V to power the relay activation line.
• Run a second wire from the 'S' lug on the starter to the switch. This allows the fuel pump to run when the engine is cranking.
• Connect the 'P' on the oil pump switch to the '86' connector on the fuel pump relay.
• On the fuel pump relay, connect the '87' to the fuel pump, and the '85' to ground.
• The ''30' on the fuel pump relay is your power source for the fuel pump. Connect it to a power source that can supply enough amps, such as the battery side of the starter solenoid.

Remember to use the correct wire gauges and to crimp all electrical connectors securely to avoid malfunction and electrical fires.

How to wire the '30' on the fuel pump relay

To wire the 30 on the fuel pump relay, you will need to run a dedicated wire from your battery to pin 30 on the relay. This is because the 30 pin is the power source for the fuel pump.

It is important to note that you should use a relay that can handle the amperage your fuel pump will pull. Using a relay that cannot handle the amperage may damage the relay and cause it to fail. It is recommended to use 14-gauge wiring or larger, depending on the amperage requirements of your fuel pump.

The fuel pump relay typically has 4 pins labelled 30, 85, 86, and 87. Here is a step-by-step guide on how to wire the fuel pump relay:

• Wire pin 85 of the relay to the 12v supply wire from the ECU. This will energize the relay to turn on.
• Wire pin 86 to a good ground on the vehicle. Ensure you use appropriately sized wire to avoid burning up the relay.
• As mentioned earlier, run a dedicated wire from your battery to pin 30 on the relay.
• Finally, run a wire from pin 87 to the factory wire that runs to the fuel pump.

By following these steps, you will ensure that the fuel pump receives a consistent and clean voltage supply directly from the battery, improving its performance and efficiency.

How to wire the '87' on the fuel pump relay

To wire the 87 on the fuel pump relay, you need to understand the function of the relay and the role of each pin. The relay acts like a light switch, and the pins are usually labelled 30, 85, 86, and 87. Here's a step-by-step guide on how to wire the 87 on the fuel pump relay:

• Understanding the Relay: The relay is an electrically operated switch that controls the fuel pump's power supply. It ensures a consistent and clean voltage supply to the fuel pump, improving its efficiency and preventing issues caused by voltage fluctuations.
• Identify the Pins: Pin 30 is the power input, which is connected directly to the battery. Pin 85 is the control input, which receives a 12V signal from the stock ECU. Pin 86 is the ground connection, ensuring a good and clean ground for the relay. Pin 87 is the output, which is connected to the fuel pump.
• Wiring the 87 Pin: To wire the 87 pin, follow these steps:

• Cut the 12V supply wire from the ECU to the fuel pump, creating two halves: one running to the fuel pump and the other to the ECU.
• Connect pin 87 to the half of the wire that runs to the fuel pump. This establishes a direct connection between the relay and the fuel pump.
• Ensure you are using appropriately sized wires for all connections.

Completing the Circuit:

• Connect pin 30 to the battery, providing a dedicated voltage line.
• Connect pin 85 to the 12V supply wire from the ECU. This energizes the relay to turn on.
• Connect pin 86 to a good ground on the vehicle.

Testing: Once the wiring is complete, test the circuit:

• With the ignition turned on, the relay should receive a 12V signal on pin 85, activating the relay.
• Pin 87 should now have continuity with pin 30, providing a clean voltage supply to the fuel pump.
• When the car is shut off, pin 85 loses the 12V signal, deactivating the relay and cutting the voltage supply to the fuel pump.

By following these steps, you can properly wire the 87 on the fuel pump relay, ensuring a reliable and efficient power supply to the fuel pump.

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