Hardwiring a High-Flow Fuel Pump with a Dedicated Relay (Honda/Acura)

Lay out all materials before starting: 10 AWG lead and ground cable, a 10 AWG inline fuse holder, a 40 A automotive relay, OEM Honda spade connectors for the fuel pump plug (part no. 07692-0011000 - buy extras in case of a bad crimp), 12-10 AWG female spade connectors, a 3/8 in ring terminal, 25 A ATC fuses, fire-retardant wire conduit, heat shrink, electrical tape, and rosin flux. A high-wattage soldering station is important: 10 AWG wire sinks a lot of heat, and the author ran his iron at about 750 F to get solder flowing within roughly 5 seconds.

Remove the plastic kick panel covering the ECU, then pull the floor mat and carpet out of the way and remove the plastic trim holding the carpet. This exposes the area behind the passenger-side glove box and the path along the floor to the rear seat.

Cut about 10 ft of 10 AWG lead cable for the run from the battery to the back of the car. Feed it through the firewall grommet close to the battery; it emerges under the passenger side, behind the glove compartment and A/C components. Route it through the long green bracket that carries the OEM wiring harness back to the area behind the passenger seat. Inspect the insulation every couple of feet as you pull it through - a hidden chafe here creates a short that is very difficult to find later. Leave slack at both ends so you can re-terminate if a joint goes wrong, then refit the carpet, mat, and plastics.

Strip a short length of insulation from the cabin end of the new battery cable and slide heat shrink well down the wire so soldering heat cannot shrink it prematurely. Crimp on a female spade connector, apply rosin flux, and solder the joint - with the iron at around 750 F the joint should wick solder in about 5 seconds. Do not touch or bend the joint until it has fully cooled; disturbing it creates a cold joint and a poor connection. Once cool, slide the heat shrink up and shrink it. This new battery feed connects to terminal 30 on the relay.

Find the original fuel pump power wire at the rear of the car (yellow with a green stripe on this 1999 Integra) and cut it, leaving enough length at the plug side to work with and to fit heat shrink. Terminate it with a female spade connector: crimp, solder, and heat shrink. Use a short piece of heat shrink over just the soldered area first, then a longer piece over the whole termination for double protection. This original power wire becomes the relay trigger and connects to terminal 85. If you want a hidden fuel kill switch, extend this trigger wire with 16 or 18 AWG wire, route it through the switch, and then on to pin 85.

Locate the original fuel pump ground wire (black with a white stripe and single silver dots on this car) and repeat the same process: cut it with workable length, strip, crimp a spade connector, solder, and heat shrink. This original ground completes the relay coil circuit and connects to terminal 86. Slide a larger piece of heat shrink over each spade connector, plug it onto the relay, then shrink it so no bare terminal remains exposed.

Remove the cover over the fuel pump hanger assembly. Run new 10 AWG power cable and 10 AWG ground cable (the same gauge as the battery feed) through the rubber grommet on top of the hanger. These will replace the undersized factory wiring between the plug and the pump.

Crimp the OEM Honda spade connectors (part no. 07692-0011000) onto the new power and ground cables. Crimping 10 AWG into these terminals is a very tight fit, but they can be crimped, soldered, and heat shrunk successfully. Cut the OEM plug off the fuel pump hanger pigtail, de-pin it, and insert the new terminals - the ground goes in the position nearest the press-in retainer. Make sure each terminal locks in place and cannot be pulled out, then reconnect the plug and refit the hanger cover.

On the new power wire coming out of the hanger grommet, crimp, solder, and heat shrink a female spade connector. This wire, running from the fuel pump to the relay, connects to terminal 87. At this point the relay wiring is complete: battery feed on 30, original pump power (trigger) on 85, original pump ground on 86, and new pump feed on 87.

Take the new ground cable exiting the grommet and terminate it with an uninsulated 3/8 in ring terminal - crimped, soldered, and heat shrunk. Run it to the bolt holding the seat belt clip to the chassis. Before bolting it down, clean the contact area to bare metal with coarse sandpaper; a clean, low-resistance ground is essential for a high-current pump.

In the engine bay, splice the 10 AWG inline fuse holder into the new battery feed close to the battery: cut, strip, solder, and heat shrink both joints. Attach a ring terminal on the battery side using the same crimp-solder-heat shrink method, then cover the run with fire-retardant conduit. Fit a correctly sized fuse (25 A ATC used here) only when wiring is complete.

Back inside the car, probe the new fuel pump plug with a voltmeter: red probe in the power terminal, black probe on the ground terminal. Confirm the fuse is installed and any kill switch is on, then turn the ignition key to ON without starting the engine. You should read battery voltage at the plug. If you do, the hardwire circuit is complete and ready for the new pump to be wired to the hanger.