Stock fuse box or aftermarket fuse box?

I'm at the very beginning of the planning stage of rewiring project for a Subaru Impreza WRX STI Type-RA (MY97 V3). Should I use the stock fuse boxes or should I run new fuses boxes? The overall approach is to create the engine harness first and then eventually redo the entire car's body harness (an ambitious goal with lots of work). So, what would be the best choice for a street build -- stock fuse box with additional custom fuse box, or full custom fuse box?

If you guys could share some insight based on your experiences, I'd appreciate it thanks.

(Edited 2025-10-22: Edited and reduced for clarity and simplicity)

What is the purpose of the car? If it's a street car, driven regularly, I would just repair/replace anything that is broken or proven unreliable. Use the stock fuse box, and existing wiring as much as possible.

If it's a show car, with hidden wiring, and perhaps new technology like PDM replacement for fuseboxes. Then you may use the existing fuse box, relocate and replace with something else.

If it's a race car, with a stripped interior and lots of systems/functionality removed. Then I would do a ground-up harness, perhaps relocating the fuses / relays (or PDM) to somewhere easy to access / service.

Very interesting approaches. It's a street car. Goal is to build it out to a high-performance street car. It won't be 100% stock.

Future mods:

• 300-400 HP (from stock 250-270HP)

• Street car (full interior, stock fuel tank, AC)

• Possible add: Flex fuel sensor

• Aftermarket boost controller (replaces stock boost controller)

• Possible add: Aftermarket knock sensor (replaces stock knock sensor)

• Uprated fuel injectors

• Spare CAN connector in engine bay

• CAN hub in cabin interior

• ECU: Haltech Platinum Sport 1000

When it comes to street build, might I infer why we should make repairs/fixes with a street build?

First, IMHO, we may not completely know or understand the wattage or current rating of some components in systems such as the AC system, so it is best to retain the OEM's electrical system design.

Second, there's less work involved and less complexity (adhering to the 'Keep It Simple, Stupid' rule).

If you could let me know what you think, thanks

For a street car -- If your tail lights and brake lights are working, why would you want to put in new wiring and connectors? But you start to, then you realize that the harness also carries the back up lights, turn signals, license plate light, trunk light and who know what else. If it's working, perhaps clean things, add more protection where a wire may want to rub something -- but there is very little advantage to removing and replacing the wiring just to have the same functionality.

Now perhaps you need a higher capacity fuel pump, and the OEM wiring isn't up to the task. I would just run separate wiring to the fuel pump. Leave the existing fuel level wiring if it's working.

Behind dash wiring is another case where the factory has wired up all the switches and controls -- if they are working, it's much easier to keep that, than to try and understand every control, inputs, connector (but it's good to have the complete factory wiring diagram so if you do need to debug, you have all the necessary info).

I've worked on many production based race cars -- often 50% or more of the original wiring is still used (particularly for things like brakes, blowers / defrosters, and often instrumentation. We may add extra for a data-logging dash, but if the OEM wiring provides wheel speed data on the CAN bus, why do any extra wiring?

Your build sounds like stock+ So I would just make all the new additional working be as professional as possible. If you're going to have engines in and out, then an engine harness with just one or two bulkhead connections is a real convenience.

Okay, I understand now. Thank you for your insight. Very helpful stuff. It sounds like the general mode of thinking is 'What advantage can I gain with this change?', keeping things simple, and being smart about our approach.

That is an excellent summary of my suggestion. Good for you to get that from my rambling....