How to Hardwire a Fuel Pump to Battery
By DeatschWerks | Published: 2026-10-18
Category: How-to Guides
Step-by-step guide to hardwiring a fuel pump directly to the battery using a fuel pump hardwire kit. Learn the process, common mistakes, and which DeatschWerks kit fits your setup.
Quick answer
Hardwiring your fuel pump directly to the battery with a dedicated fuel pump hardwire kit bypasses the factory wiring, ensuring stable voltage and preventing voltage drop under high load.
Why hardwire a fuel pump?
Factory fuel pump wiring is often undersized for high-output pumps, especially in modified or high-performance cars. Voltage drop at the pump reduces flow and pressure, which can lean out the air-fuel mixture under boost. A dedicated hardwire kit uses thicker gauge wire and a relay to deliver full battery voltage directly to the pump.
How to hardwire a fuel pump to battery
- 1. Disconnect battery negative terminal: Always start by disconnecting the negative battery cable to prevent accidental shorts or sparks while working with live power. Verify the battery is disconnected before touching any wiring.
- 2. Mount the relay and fuse holder: Choose a clean, dry location near the battery. Secure the relay and fuse holder (included in DeatschWerks kits) with screws or zip ties. Ensure the fuse is within 18 inches of the battery positive terminal. A loose relay can short against metal; use rubber grommets if mounting through sheet metal.
- 3. Route power wire from battery to relay: Run the red power wire from the battery positive terminal to the relay's #30 terminal. Use the supplied fuse holder inline. Keep the wire away from exhaust heat and moving parts. Check for chafing points; use split loom or heat shrink where the wire passes through metal.
- 4. Connect relay trigger wire: Connect the relay's #86 terminal to a switched 12V source (e.g., fuel pump fuse or ECU output). Connect #85 to chassis ground. This ensures the relay only activates when the ignition is on. Using an unswitched source will drain the battery; confirm the trigger wire is ignition-switched.
- 5. Run output wire to fuel pump: Connect the relay's #87 terminal to the fuel pump positive wire. Use the supplied connectors and heat shrink. For dual-pump setups, use the DeatschWerks Dual-pump Universal Kit which provides separate outputs. A poor crimp connection here is the most common failure point; use a ratcheting crimper.
- 6. Ground the pump and relay: Connect the fuel pump ground wire directly to the battery negative terminal or a clean chassis ground. The relay's ground (#85) should also be clean and tight. Grounding to painted or rusty metal will cause intermittent pump operation; scrape to bare metal.
- 7. Test the system: Reconnect the battery. Turn the ignition to ON (do not start) and listen for the fuel pump prime. Check voltage at the pump connector with a multimeter—it should read within 0.2V of battery voltage. If the pump doesn't prime, check the relay trigger signal and fuse before assuming a bad pump.
Fuel pump hardwire kits from DeatschWerks
- High-current Universal Kit to Hardwire Fuel Pump to Battery: This High-current Universal Kit to Hardwire Fuel Pump to Battery is a fuel pump hardwire upgrade kit designed to connect a fuel pump directly to the battery. It supports higher current demands, making it ideal for single high-flow pumps in boosted applications.
High-current Universal Kit to Hardwire Fuel Pump to Battery - Universal Kit to Hardwire Fuel Pump to Battery: The Universal Kit to Hardwire Fuel Pump to Battery is a standard hardwire kit for connecting a fuel pump to the battery. A cost-effective solution for single-pump setups that need a reliable direct battery connection without extra current capacity.
Universal Kit to Hardwire Fuel Pump to Battery - Dual-pump Universal Kit to Hardwire Two Fuel Pumps to Battery: The Dual-pump Universal Kit to Hardwire Two Fuel Pumps to Battery is designed to hardwire two fuel pumps to the battery. Perfect for dual-pump systems (e.g., surge tanks or staged pumps) where each pump needs its own dedicated circuit.
