Hard wiring a fuel pump

The benefit of hard wiring your fuel pump (connecting it directly to the battery) is to give it a constant power supply rather than the OE wiring which can give varying voltage depending on loads, sometimes less than 11V, which obviously will affect flow rates. Constant supply will give a constant flow and therefore the best performance from the pump.

Hard wiring kits can be bought relatively cheaply from places such as www.apexperformance.co.uk , but all they are is a few lengths of wire, a fuse and a relay, easily sourced and bought for less – www.maplins.co.uk , www.ebay.co.uk , http://www.vehicle-wiring-products.eu/VWP-onlinestore/home/homepage.php

How much wire you need depends on how far away your battery (or a decent power source such as ICE power cable) is – if your battery is in the boot then it makes this job much easier. The power cable needs to be a good thickness, about 10awg should be plenty, to ensure there is no voltage drop along it.

A 12v 30Amp 4 pin relay will be sufficient for the job of switching the power to the pump – to connect to the relay you can either use crimp on female spade connectors or relay sockets are available, supplied with connectors or pre-wired, which look a lot neater.

Inline blade fuse holders are available in several types – supplied with either a length of wire or spade terminals either side or that snap on to the wire ends (like a scotchblock). Check and see what the original fuel pump fuse is and use the same value, a 30A fuse should be sufficient.

If the battery is in the boot and the relay is close by then a fused relay can be used instead.

All joints should either be soldered and heatshrunk (or wrapped in electrical tape) or crimped butt connectors.

To wire everything up you must first determine which original fuel pump wire is the +ve. Disconnect the plug and using a multi-meter either find which one has continuity to ground – that will be the –ve wire, or with the ignition on which one has power.

With the ignition off and battery disconnected cut the fuel pump +ve wire a few inches from the plug. Strip back a bit of the wire left on the plug and solder (or crimp) on a length of wire – this needs to be long enough to reach the relay, which should be mounted to the bodywork close by.

The original fuel pump wire will now be used as the trigger feed to the relay. If it is long enough to reach the relay then just crimp on a female spade connector, otherwise extend the wire first.

Fit the fuse in the new supply wire close to the battery and connect one end to the battery +ve clamp, then run it safely out of the way through the car to the relay.

The relay earth cable needs a ring terminal crimping to one end which should be attached to a good grounding point – a mounting hole in the bodywork with paint cleaned off, using the same place the relay is fixed to is a good idea.

You should now have four wires that need to be attached to the relay, here’s how…

The original fuel pump supply wire should be attached to pin 85.

Ground wire to pin 86.

The new 12V supply to pin 30.

And the wire from the fuel pump to pin 87.

With those all connected and routed out of the way reconnect the battery and try to start the engine – it should fire as normal, if not then check for loose connections or the fuse