m3chhawk

Introduction
The following DIY should help you build and install your own fuel pump relay harness. This harness/kit is available from certain vendors, but you can build it yourself for about half the price using parts found at your local auto parts store.

High fuel flow rates (500+ HP) require more power than the factory power wires can supply to the fuel pump. This can lead to unstable voltages which in turn result in unstable fuel pressure. This harness provides a dedicated circuit using larger gauge wiring over a much shorter run.

Disclaimer
If you choose to do this DIY following these instructions, you are doing so at your own risk. This harness is inherently safe if built and fused correctly.

Theory of Operation
This section is for those that do not understand exactly what is going on with the install and operation. Most of you can ignore it so it is hidden behind a spoiler.


Parts List

• (1) 4-pin 30A 12 Volt Automotive Relay
• (12 feet) 12 AWG Primary 12V Wire (Red)
• (8 feet) 18 or 20 AWG 12V Wire (Pink, Red, or White. I used red. The factory wiring you are replacing is pink.)
• (8 inches) 18 or 20 AWG 12V Wire (Black)
• (1) in-line fuse holder with 12 AWG leads (I recommend an ATO blade fuse holder with a cap)
• (1) 30A fuse (I recommend a spare for the glove box as well)
• (~8 feet) wire loom
• (~1 foot) 1/4" heat shrink tubing
• (2) 3/8" ring terminal connectors (14-16 AWG)
• (4) female spade connectors (14-16 AWG)
• (1) self-tapping machine screw (1/4x20)
• electrical tape

I had a lot of the stuff laying around, but you should be able to find everything you need at your local auto parts or hardware store for $30-$40.

Tool List

• Soldering iron and solder
• Heat gun, handheld torch, or lighter
• Wire cutters
• Wire strippers
• Ratchet with 10mm socket
• Razor blade or razor knife
• Large phillips screwdriver (for poking hole in factory grommet)
• Small flat screwdriver (for plastic clips)
• Interior panel removal tool (optional)

Instructions
STEP 1:
Start by building the power side of the harness. The picture describes this best, but the steps are listed below:

• 12" lead (12AWG red) with ring terminal on one end soldered to fuse holder on the other. You must use a 3/8" ring terminal here. 1/4" will not fit for the battery terminal.
• Solder the other end of the fuse holder to a 3' lead (12AWG red) with a spade terminal on the other end.
• Heat shrink all your connections.

Note: You can use 14-16 AWG spade terminals and ring connectors with the 12 AWG wire, but you may need to spread the connector opening a bit with a pick to get the wire in before crimping.


STEP 2:
You now need to gain access to the battery compartment. You will need to remove the windshield cowl, the battery cover door, and the battery trim. The cover door comes off by depressing the clip. Then the trim piece is held in by a few plastic clips. The cowl can be a bit tricky. There are a few more clips and it hooks to the driver side cowl. There is also a small tab that connects it to the rubber vertical trim piece on the windshield.


STEP 3:
With the battery covers out of the way, you want to disconnect the negative battery terminal. Note: The fuse holder should be empty before proceeding with the next step. Now pull the red plastic cover off the positive terminal and connect the ring terminal on the power side the harness to the stud closest to the passenger side of the vehicle.

Route the cable around the front of the battery and around to the passenger side. Now you will need to poke a small hole in the factory firewall grommet. I did this by starting a small slit with an exacto knife and then pushing a large screwdriver through the hole. Once you have the hole punched, push the spade terminal end of the harness through the hole and into the cab. Keep pushing the wire through until nearly all of the harness is in the car. Keep a little bit of slack in the battery compartment. When done, the fuse holder should tuck up nicely inside the rubber hood as pictured.

Note: you probably won't have this many wires running through your grommet. I have all my sensor wires for my EBC, boost gauge, wide band, and oil sensors ran through the same grommet.
Now you want to notch the red cover with a razor blade or knife so the wire can come through. There is a small clip on the side of the cover and you can to cut the notch just on the battery side of this cover. My notch is a little bigger than necessary and I ended up cutting that tab off. Re-install the red cover. Pictured above.

STEP 4:
Move to the interior of the car. Push your passenger seat all the way forward and remove the compartment (pull out and down) and "shelf" in the area behind the seat. Once removed you need to pull out the insulation material. This will expose the fuel pump access lid. It is held in with (4) 10 mm bolts. Once loose, pull the door up and disconnect the main harness plug on the inside. It should now look like this:


STEP 5:
Take your remaining 12 AWG red primary wire (should be about 8' at this point) and an equal length run of your 18-20 AWG wire. Tape the ends together using electrical tape so they can be fished to the rear together. The easiest way for me to do this was through the interior piece below the seat belt holder. You want to fish them through to the fuel door compartment.


STEP 6:
Now you need to cut the pink wire on the fuel pump electric harness. It may be easier to pull the grommet out of the cover (as pictured). Remove the electrical tape around the loom and pull the pink wire from the protective loom. I cut the wire in the middle to give me room to work on each end.

Now you need to solder the two wires that you just pulled through. The larger wire (12 AWG) will go on the pink wire going to the connector (fuel pump side). The smaller wire will go to the other side (harness side).

Heat shrink your connections. Re-install the grommet and cover. Tape up your wires to each other ensuring they aren't in a bind and aren't easily pulled apart.


STEP 7:
Remove the tunnel cover just inside the door sill. It is held in with interior clips and should easily pull straight up.

Remove the passenger side kick panel. There is a small nut up by the firewall that can be removed by hand. The panel should then pull straight out with interior clips.

Back to the two wires at the rear. Tape them together every foot or so and then wrap them in wire loom. I used spiral wrap because I had it. You can also use the split loom similar to the style at the fuel pump.

Tuck the wire harness behind the rear interior piece and in the exposed wire track.

You can now re-install all of the rear interior pieces.

STEP 8:
Create the ground wire. It needs to be about 6-8" with a spade on one end and a ring terminal on the other. This wire size should be the same gauge as the small wire from the fuel pump (or larger, but not smaller). Make sure to heat shrink the connections.


STEP 9:
You may need to shorten the wires pulled from the rear. Note the relay location below and make sure your wires are the appropriate length. Add spade terminals to the two wires pulled from the rear and heat shrink. Locate the large red primary wire that was pushed through the firewall in step 3. It will be tucked up top right behind the kick panel. You may have to search a bit. Now connect all wires to the relay as listed below:

• Terminal 30 - to the larger power wire (coming from the rear) that was connected to the fuel pump side of the pink wire.
• Terminal 85 - to the smaller power wire (coming from the rear) that was connected to the harness side of the pink wire.
• Terminal 86 - to the ground wire created in step 8.
• Terminal 87 - to the power wire coming from the battery.

Now screw the relay to the wall behind the kick panel using a self tapping screw as shown. I also put a large piece of shrink wrap around all of the connections and zip tied all of the wires together.

Run the ground wire to the bolt holding the control module to the wall with the 10 mm bolt (pictured above). Tie up and secure all wires using zip ties.

STEP 10:
Install the 30A fuse in the holder and re-install the negative battery cable.
It is now time to test the relay. Place your hand on the relay and place the ignition in the "ON" position. You should feel the relay "click" if everything on the power side is connected correctly. If not, check your ground connection, the power connection to the battery, and the fuse.
You should now be able to start the car. If everything fires up, you are good to go. If not and the relay is in fact turning on (clicking), check your connections at the relay where it runs to the fuel pump and then at the fuel pump. If all checks out, re-install interior panels (don't forget the nut on the kick panel) and all battery compartment covers. Push the fuse holder back up under the rubber hood to protect it.

Enjoy! Let me know if you have any questions/comments/suggestions. I am open to all.

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