Electrical Upgrades Beyond Basics: Relays, Fuses & Wiring Harnesses

Once you've handled the starter, alternator, and battery, it's time to look deeper into your Honda Acty’s electrical system—the often-overlooked components that affect everything from lighting reliability to accessory performance. If your wiring is brittle, fuses keep blowing, or you’re planning to add high-draw components (like light bars, winches, or upgraded horns), this guide walks you through essential electrical upgrades beyond the basics: relays, fuses, and wiring harnesses.

🔌 Why These Upgrades Matter

Older kei trucks like the Acty weren’t designed for modern accessories. Aging wires, outdated fuse blocks, and a lack of relays can result in:

• Flickering or dim lighting

• Overheated switches

• Constant blown fuses

• Melting connectors

• Random electrical gremlins

Whether you’re restoring reliability or adding power-hungry mods, a clean and upgraded system is key.

1. Relays: Take the Load Off Your Switches

A relay is an electrical switch that allows a small current to control a larger one. This protects fragile dashboard switches and ensures stable power delivery.

Why install relays?

• Prevent headlight dimming

• Support high-power accessories (fans, horns, lights)

• Eliminate overheating at the switch or wire level

Common Acty Relay Upgrades:

• Headlight relay harness (reduces voltage drop to halogen or LED bulbs)

• Electric fan relay kit (essential for custom cooling setups)

• Accessory relays for audio systems or fog lights

🧰 Oiwa Tip: Use a 4- or 5-pin automotive relay with proper fused power input. Always use heat-shrink connectors for weather resistance.

2. Fuses: Old Blocks vs. Modern Protection

The factory Acty fuse box is serviceable, but not designed for expansion or high current loads. Many imports show signs of corrosion, cracked covers, or burnt terminals.

Upgrade Options:

• ✅ Inline waterproof fuse holders – for direct-to-battery accessories

• ✅ Blade-style fuse panels – replace old glass tube or mini fuses

• ✅ Resettable circuit breakers – great for winches and power inverters

• ✅ Add-a-fuse adapters – safe way to piggyback new circuits into the cabin

Fuse Tips:

• Match amp rating to wire gauge and load

• Always fuse as close to the power source as possible

• Replace all cracked, corroded, or loose fuse holders

📦 Oiwa Garage carries compact fuse boxes ideal for mounting behind the dash or under the seat in HA3/HH3 models.

3. Wiring Harnesses: Replace or Reinforce

From headlights to the rear tailgate, the Acty’s original wiring can become brittle and unsafe after 30+ years of heat, water, and vibration.

When to replace a harness:

• Brittle insulation, exposed copper

• Rodent damage or melted sections

• Intermittent electrical failures

• Upgrading to LED systems or higher-draw equipment

Options:

• OEM harness repair kits – with correct connectors for plug-and-play repair

• Custom harness builds – for engine swaps, off-road builds, or stereo upgrades

• Headlight or taillight rewire kits – designed for LED conversions or lifted trucks

🛠️ Pro Tip: Use tinned copper wire, soldered joints, and braided loom for longevity—especially in rear-engine Actys with exposed underbody wiring.

Bonus: Grounds & Connectors

Poor grounds cause 90% of weird electrical issues in older cars.

Checklist:

• Add new ground straps (battery to chassis, chassis to engine)

• Sand paint off ground locations before mounting

• Use star washers or grounding lugs for secure contact

• Upgrade connectors to weather-sealed (Deutsch, Metri-Pack, or waterproof spades)

🔋 Oiwa Tech Tip: Use a multimeter to test voltage drop across grounds while cranking or under load—over 0.2V means it's time to clean or upgrade.