Connecting Fuel Pump To Oil Pressure Switch: A Guide

Hooking up a fuel pump to an oil pressure switch is a common modification for car enthusiasts. This modification can increase safety and prevent engine damage in the event of a crash or low oil pressure. The process involves wiring the fuel pump through an oil pressure safety switch, which is typically screwed into a 1/8-27 NPT oil pressure port on the engine. The oil pressure switch acts as a failsafe device, cutting off the fuel pump if the engine loses oil pressure. This can be achieved using a relay to minimise voltage drop and ensure maximum output. A diagram and instructions for this setup can be found online.

The oil pressure switch as a safety device

The oil pressure switch is a crucial safety device in any vehicle. It is designed to protect your engine by monitoring the oil pressure and taking action if the pressure drops below a certain threshold. This system is essential for preventing engine damage and even potential fires in the event of an accident.

The oil pressure switch is typically located near the oil filter or the engine block, connected to the engine's oil pressure system. When the engine is running, the oil pump circulates oil, creating pressure. This pressure is then sensed by the oil pressure switch. The switch has a diaphragm mechanism that responds to changes in oil pressure.

When the oil pressure drops below the predetermined threshold, the diaphragm inside the switch moves, completing an electrical circuit. This action triggers a warning light or alarm on the dashboard, alerting the driver to the low oil pressure condition. Additionally, in some systems, the oil pressure switch can interrupt the fuel pump, causing the engine to stall and prevent potential damage.

It is important to note that the oil pressure switch only provides a binary output, turning the warning light or alarm on or off. If you want continuous feedback on the oil pressure, you would need to use an oil pressure sensor, which provides a numerical value of the pressure reading.

To ensure the proper functioning of the oil pressure switch, regular maintenance is key. This includes regularly changing the engine oil, using high-quality oil and filters, and inspecting for leaks. By taking care of these aspects, you can prolong the life of your oil pressure switch and maintain the health of your engine.

In conclusion, the oil pressure switch serves as a vital safety measure in your vehicle. By responding to changes in oil pressure, it helps prevent engine damage and keeps you informed about the engine's health, allowing you to take appropriate action when needed.

How to wire the oil pressure switch

Wiring an oil pressure switch to a fuel pump can be a safety measure to prevent engine damage and fires in the event of an accident. The process involves connecting the oil pressure switch to the fuel pump relay, which in turn controls the fuel pump. Here is a step-by-step guide on how to wire the oil pressure switch:

Step 1: Understanding the Oil Pressure Switch

The oil pressure switch is a single-pole, double-throw switch that controls the power supply to the fuel pump. It has three terminals: Normally Open (NO), Normally Closed (NC), and Common (C). The NO contact is open when there is no oil pressure and closes when the oil pressure reaches a certain threshold. The NC contact is closed when there is no oil pressure and opens when the pressure rises. The C terminal is connected to the fuel pump relay.

Step 2: Connecting the Oil Pressure Switch to the Fuel Pump Relay

The oil pressure switch is wired in parallel with the fuel pump relay. The NO terminal of the oil pressure switch is connected to a 12V source, which provides power to the fuel pump when the ignition is turned on. The NC terminal is connected to the "S" terminal on the starter solenoid, which provides power to the fuel pump during cranking. The C terminal is connected to the yellow wire on the fuel pump relay.

Step 3: Wiring the Fuel Pump Relay

The fuel pump relay is connected to the battery, fuel pump, and ground. The red wire (10 GA) from the relay is connected to the battery through a circuit breaker. The purple wire (18 GA) from the relay is connected to the fuel pump. The grey wire (18 GA) is connected to the ground. The yellow wire (18 GA) is connected to the oil pressure switch, as mentioned in Step 2.

Step 4: Additional Considerations

It is important to fuse all the connections to protect the circuit. Additionally, some vehicles may have an “I” terminal on the starter solenoid, which provides 12V only when the starter is engaged. This wire can be connected to the pump feed side of the oil pressure switch to prime the fuel pump during cranking.

Step 5: Testing and Troubleshooting

Before starting the engine, use a multimeter to test the continuity of the wiring. Ensure that the oil pressure switch is functioning correctly by checking the pressure at which the contacts change state. If there are any issues, double-check your wiring connections and refer to the oil pressure switch and fuel pump relay diagrams.

Using a relay to hook up the fuel pump

Step 1: Understand the Basics

Before you begin, it's important to understand the role of a relay. Think of a relay as a heavy-duty remote-control switch that can handle high-current accessories like a fuel pump but is controlled by a much smaller current. The relay is installed between the power source and the fuel pump, allowing you to turn the pump on and off.

Step 2: Gather the Necessary Parts

You will need a few key components for this project:

• A fuel pump relay: Look for a 40-amp ISO NO/NC (Normally Open/Normally Closed) relay to minimize voltage drop. You can find these at automotive stores or online.
• An oil pressure safety switch: This acts as a failsafe device, turning off the circuit if the engine loses oil pressure or in the event of a crash.
• Wiring and connectors: Ensure you have the correct gauge wiring for your setup. You may need heavy-gauge electrical wire for high-current devices like the fuel pump.

Step 3: Mount the Relay

Mount the relay as close to the battery as possible. This will help minimize voltage drop. Install an inline fuse or a fusible link that is appropriate for the high-amp, power-feed line.

Step 4: Connect the Relay to the Power Source

Connect the relay to the battery, which serves as the power source. Typically, the high-power battery-positive input terminal (often labelled "30") connects directly to the battery.

Step 5: Wire the Fuel Pump to the Relay

Using the appropriate gauge wiring, connect the fuel pump to the high-power output terminal on the relay (often labelled "87"). This provides a direct path for power to flow from the battery to the fuel pump when the relay is energized.

Step 6: Install the Oil Pressure Safety Switch

The oil pressure safety switch is typically a three-terminal switch. One terminal (often "S") connects to the starter relay or solenoid. Another terminal (often "I") receives key power or is connected to the ignition switch for cranking. The third terminal (often "P") is the active terminal when there is oil pressure.

Step 7: Wire the Oil Pressure Safety Switch to the Relay

Connect the oil pressure safety switch to the relay. The "P" terminal on the switch connects to the relay terminal that activates the relay (often labelled "86"). This low-power circuit only requires a small amount of current to function.

Step 8: Test the Setup

With the ignition in the "run" position, the engine oil pressure should close the switch, completing the circuit and energizing the relay. This, in turn, allows power to flow directly to the fuel pump. When the engine stops running and oil pressure drops, the oil pressure switch opens, de-energizing the relay and shutting down the fuel pump.

Tips and Troubleshooting:

• Always use a fuse or fusible link appropriate for the amperage of your setup to prevent electrical fires.
• If your fuel pump runs constantly, check your wiring. Ensure the "S" terminal is connected correctly and that you are not picking up a constant 12V source from the starter relay instead of a 12V source during cranking.
• If you experience issues with the oil pressure safety switch, consider using an inertia safety switch as an alternative.

By following these steps and troubleshooting tips, you can successfully hook up your fuel pump using a relay and oil pressure safety switch, ensuring both maximum output and safety for your vehicle.

The oil pressure switch and fuel pump relationship

There are a few ways to solve this problem. One way is to use a separate bypass switch. Another option is to use a Chevrolet Vega-type oil pressure switch, which has a wiring diagram available online. A third option is to use the ""I" terminal on older GM starters, which is electrically isolated from the starter energize post and will not cause any backfeeding issues.

Additionally, you can use a dual switch with both Normally Open (NO) and Normally Closed (NC) terminals. This will ensure that the circuit is only powered when needed, and will not keep the fuel pump running in the event of low oil pressure, which could result in engine damage.

The oil pressure switch sends a signal to the fuel pump relay and the dashboard when the oil pressure gets low, causing the pump to quit. This is an important safety feature, especially in the event of a collision, as it will cut the fuel pump if the engine is dead.

The oil pressure switch and fuel pump wiring diagram

Wiring an oil pressure switch and a fuel pump together involves several steps and considerations. The oil pressure switch is designed to cut off the fuel supply in the event of low oil pressure or a collision, serving as a safety feature. Here is a detailed guide on wiring the oil pressure switch and fuel pump:

Understanding the Oil Pressure Switch:

The oil pressure switch is typically a three-terminal device with Normally Closed (NC), Common (C), and Normally Open (NO) contacts. The switch activates when oil pressure reaches a certain threshold, usually around 5-6 psi. When the oil pressure drops below this point, the switch cuts off the fuel supply to prevent engine damage.

Wiring Diagram Components:

• Oil Pressure Switch: This is the three-terminal switch that will be installed in the engine, often near the oil pressure sensor or gauge.
• Fuel Pump: The electric fuel pump needs to be wired through the oil pressure switch to ensure it turns off in case of low oil pressure.
• Relay: A relay is not mandatory but can be used to ensure full voltage to the fuel pump and facilitate hot-wiring the pump for testing.
• Fuse: A fuse is recommended to protect the wiring and components in case of electrical faults.
• Ignition Switch: The ignition switch provides power to the fuel pump when the key is turned to the "on" or "start" position.
• Starter: The starter motor engages when the key is turned to the "start" position. The oil pressure switch can be wired to the starter's "S" terminal or the battery lug.

Wiring Instructions:

• Connect the NC terminal of the oil pressure switch to the starter. This allows the fuel pump to run during engine cranking.
• Wire the NO terminal to a 12V switched source from the ignition. This provides power to the fuel pump when the key is turned on.
• Connect the Common terminal to the fuel pump. This completes the circuit, allowing the fuel pump to operate.
• (Optional) Install a relay between the ignition switch and the oil pressure switch to control the fuel pump. This can provide added convenience for testing and hot-wiring the pump.
• Ensure proper grounding of the fuel pump circuit to prevent electrical issues.
• Test the wiring by turning the key to the "on" and "start" positions. The fuel pump should run during cranking and continue running after the engine starts, provided there is sufficient oil pressure.

It is important to follow the wiring diagram specific to your vehicle and consult a professional if you are unsure about the process.

Frequently asked questions