Wire Tidy and Fuse Box Relocation - Nissan S15

Today at REWIRED, we did a wire tidy on a Nissan S15 for a local custom car garage. This includes relocating the main fuse box to the boot to declutter the engine bay.

What is a Wire Tidy?

The focus on custom cars at shows is always on the paintwork, suspension, engine and all the shiny upgrades that bling out the engine bay. Unfortunately, having a tangled net of wires and ugly blocky batteries in view can take away from this. Fortunately, there is something we can do.

The main fuse box is a significantly large and dull component visible from the engine bay, with the potential to take up space or direct attention from possible upgrades. (Battery already removed)

A wire tidy can be performed at various levels. Essentially, the concept is to try and hide as many of the electrical components as possible. Though not much can be done about the vital connections to the various engine components, as they are needed whether you want to see them or not, what we can do is remove the plugs, wires, and other connectors for features that are not in use and adapt the loom in the attempt conceal what remains.

Wire tidies can also include relocations - transferring undesirable but still essential components to new locations where they can be taken out of view. Larger items, such as batteries and fuse boxes, cannot be avoided but can be relocated to areas such as the rear of the car, freeing up space and attention towards turbos and other performance items. On Nissan S15s, we have found it common to place the battery in the boot of the vehicle, with the main fuse box also being moved to the boot or instead hidden under the passenger side glove box.

A close-up of the main engine bay fuse box that the customer wants to relocate out of view.

This job has two main objectives. First, the garage wants the battery and fuse box relocated in the boot. Second, they want as many of the power harness wires hidden as possible. The stock harness runs along the left side wall of the engine bay and behind the front bumper via the top of the radiator.

The new plan is to fix the wires between the metal skins of the wings and that of the engine bay side wall, where the bulk of the harness will be out of view but still protected from the elements. Additionally, extending the wires for the frontmost section will allow us to run the cables for the lights and horn along the bottom side of the radiator rather than being visible from the top. This should declutter the vast majority of the wiring, before removing plugs and cables for features not used on this car.

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The Stock Harness

This is the stock power harness from the front of the S15. Though it makes up the majority of the wires under the engine bay, this loom is not responsible for controlling the engine itself. What this loom does control is the supply and management of power to components under the engine bay and within the cabin.

The stock power harness from the engine bay of the S15.

The fuse box is in a large plastic container under the bonnet. It holds the main fuses and relays for distributing and managing power throughout the car. Removing this outer shell reveals the sections within, which we can use to trace wires to be rerouted.

The main fuse box deconstructed from its plastic container shell.

The power harness passes from the engine bay into the cabin through a large rubber grommet. Past this grommet, there is a large white connector and a multitude of other smaller plugs that interface with the systems within the car. In order to have the main fuse box located in the rear of the car, the wires to the box will also have to pass through this grommet.

The cabin side portion of the wiring harness, separated by its bulkhead grommet.

We can see the distance from the fuse box to this Gromit. To relocate the fuse box, the wires have to be extended so that they reach the other side of the grommet, with the extra length to allow it to fit in the boot.

Showing the distance between the fuse box and the rubber grommet.

The main issue with this job is that the wires to the fuse box come from both sides of the harness. Some of the wires that need to go to the fuse box are connected to plugs already on the other side of the grommet. Rather than extending the wires from the other side of the loom, doubling back through the grommet, it will be easier to cut and feed these wires back through the grommet, removing them from the other side entirely and extending them from the cabin side of the loom. This will give the advantage of a slimmer harness, as well as maximising the already existing length of the wires. As many more wires will have to feed through the grommet than before, finding ways to slim the loom will be very beneficial.

Making the Alterations

With the tape removed, we can now identify what they are for and where they go. This will allow us to carefully pick out the wires that need extending.

Picking out the wires to the fusebox to identify and verify their purpose and where they go.

Once identified, the fuse box wires can be parted from the rest of the wiring harness, separated by what remains the same and what needs to be altered. As we can see below, some parted wires come from different directions, meaning that not every wire can be extended by the same length.

Some of these wires also belong to the front side of the car, such as the headlights and horn. These will also have to be extended the other way, to allow for the extra length so they can be better hidden under the bonnet.

Partitioning the loom by where and how wires need to be extended.

One at a time, wires that were already long enough were pulled from the engine side of the grommet through to the cabin side. For others, they have to be extended closer to the original point of the fuse box, with new wires fed through instead.

Showing a closer look at the wires being pulled through the grommet to their respective new sides.

As new wires get added to the harness, they can be taped into sections, keeping the general form of the loom. This ensures that the wires are routed and lengthened properly and that the locations of the original branched sections don't fall out of place, keeping the harness organised as we complete major changes.

Re-taping sections of the loom to keep it organised and retain its form.

A wire-holding tool can also be used to aid the soldering of these extensions. It is also good to make sure that the extensions are mostly coming from the same place and not somewhere where they are at a bend or exposed to any other stresses. It is also best to “step” the joints so they are not exactly aligned.

As joints are made and then insulated, the thickness of the wire increases at this point. If you repeat this process 20+ times, then these wires will begin to bulge and can be hard to route through the car. Slightly staggering, the placement of these joints allows for a slimmer loom and for the joints to be supported by the natural rigidity of the loom rather than introducing a new weak point. The downside is the extra planning required, as each wire needs to be extended by an individual length.

Performing a solder join on an extended wire. A soldering aid helps keep the wire in place, freeing up the other hands to create a clean join.

We also used water-resistant heat-shrink tubing to insulate the joints. These allow a tighter fit than tape and allow a more even coverage around the join. In addition to the tubing shrinking over the unique profiles of the joints, the glues inside add further support to prevent the insulation from coming loose or letting in moisture.

Finishing Touches

We can now see the additional length added to the fuse box, allowing it to reach the other side of the car. This long set of cables will start from the bulkhead side of the cabin, run concealed underneath the plastic trim alongside the driver seat, and pass into the boot space from behind the back seats.

The fuse box is now rebuilt, with the wire extensions complete.

With the loom now completed, the rest of the taping can now be performed. We can see that with enough careful planning, the length of the wires passing through the grommet is close to the original quantity.

Taping up the loom near the grommet, now the wiring alterations are complete.

With this, the alterations for the fusebox wiring are complete, ready for the final inspections.

The wiring harness is now complete and waiting for final inspections.

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