Big 3 Upgrade Step-by-Step | Fix Voltage Drop & Lights Dimming

Posted by Jacob Morris on Jun 1st 2024

The Big 3 Upgrade: How to Fix Voltage Drop, Stop Lights Dimming, and Improve Car Audio Performance

If you’re upgrading your car audio system or adding high-demand electrical accessories, the Big 3 upgrade is one of the most important electrical improvements you can make. It directly addresses common problems like voltage drop, lights dimming, and inconsistent amplifier performance by strengthening your vehicle’s main electrical connections.

Many people jump straight to bigger amplifiers, extra batteries, or a high-output alternator without fixing the real bottleneck: factory electrical wiring. The Big 3 upgrade solves that problem at the source.

This guide explains what the Big 3 upgrade is, when you should upgrade your electrical, what tools you need, and how to do the Big 3 upgrade step by step—the right way.

What Is the Big 3 Upgrade?

The Big 3 upgrade improves your vehicle’s electrical system by upgrading the three primary high-current paths using larger-gauge, lower-resistance wiring. Factory wiring is designed for stock loads, not modern car audio systems, aftermarket lighting, or other power-hungry accessories.

The three upgraded connections are:

Alternator positive → Battery positive
Battery negative → Vehicle chassis
Engine block → Vehicle chassis

Important: The factory wires are not removed. The Big 3 upgrade adds heavier wire alongside them to improve current flow.

The “Big 4” Upgrade (Recommended Extra Step)

Through real-world testing, we also recommend adding one additional ground:

Alternator bracket → Battery negative

This extra step further reduces resistance at the alternator and improves charging stability, especially on higher-power systems. While not required, it consistently improves results.

Why the Big 3 Upgrade Matters

Upgrading these electrical paths provides several major benefits:

Reduces Voltage Drop

Undersized factory wiring creates resistance under load. The Big 3 upgrade significantly reduces voltage drop, especially during heavy bass hits.

Stops Lights Dimming

Headlights dimming when the bass hits is a clear sign of electrical strain. A properly installed Big 3 upgrade often eliminates lights dimming entirely.

Improves Car Audio Performance

Amplifiers deliver cleaner, more consistent power when voltage remains stable, resulting in better sound quality and output.

Extends Electrical Component Life

Lower resistance means less heat and stress on batteries, alternators, and wiring.

When Should I Upgrade My Electrical with the Big 3?

You should strongly consider a Big 3 upgrade if:

Your system produces 1,000 watts RMS or more
You’re installing or running a high-output alternator
You experience voltage drop or dimming lights
You’re upgrading batteries (AGM or lithium)
You plan future electrical or car audio upgrades

The Big 3 upgrade should always be your first electrical upgrade, before adding extra batteries or upgrading your alternator.

Tools & Materials Needed for the Big 3 Upgrade

We offer complete Big 3 kits, but if you’re doing it yourself, here’s everything you’ll need.

Wiring & Supplies

1/0 AWG or 4 AWG power cable (depending on system power)
Copper lugs or ring terminals matched to wire size
Heat shrink tubing
Battery terminals (correct post size)
Zip ties

Tools

Wire cutters rated for large-gauge wire
Wire strippers
Heavy-duty crimpers
Solder and soldering iron (recommended)
Heat gun
Digital multimeter (DMM)
Standard hand tools (wrenches, sockets, screwdrivers)

How to Do the Big 3 Upgrade (Step by Step)

Step 1: Plan Your Wiring Routes

With the hood open, plan your wire routing carefully:

Avoid belts, pulleys, fans, and moving parts
Avoid exhaust and high-heat engine components
Choose solid mounting points that won’t vibrate

Good routing prevents failures later.

Step 2: Disconnect the Battery

Park the vehicle safely, allow the engine to cool, and disconnect the battery negative terminal first.

Step 3: Measure & Cut the Wire

Lay the wire along each planned route:

Leave an extra 1–1.5 inches for stripping and terminals
Cut all required sections before installing

Step 4: Prep the Cables

Best Method: Soldered Copper Lugs

Heat the lug and add solder
Insert the wire while solder is molten
Ensure no exposed strands
Seal with heat shrink tubing

Alternate Method: Crimped Terminals

Use a proper heavy-duty crimper
Tug test each connection
Seal with heat shrink tubing

Step 5: Install the Big 3 Wiring

Install in this order:

Battery negative → Chassis
Engine block → Chassis
Alternator bracket → Battery negative (extra step)
Alternator positive → Battery positive (connect last)

Factory wiring can remain in place or be replaced—both methods work.

Step 6: Secure the Wiring

Zip-tie wiring every 12 inches
Secure to non-moving, non-hot surfaces
Ensure wires cannot rub or shift

Step 7: Test the Electrical System

Charging Voltage Test

Using a DMM:

Normal charging range: 13.6V – 14.8V

Ground Resistance Test

Set DMM to ohms (Ω)
Battery negative → Chassis
Alternator positive → Battery positive cable end

Readings under 1 ohm indicate a solid connection.

If resistance is high:

Clean ground points to bare metal
Remove corrosion
Retest

Special Note: Big 3 Upgrade on RVC Vehicles (GM & Modern Cars)

Many newer vehicles—especially GM—use RVC (Regulated Voltage Control) systems.

What Is RVC?

RVC is a smart charging system that uses a current sensor on the factory negative battery cable to control alternator output for fuel efficiency.

How to Do the Big 3 on RVC Vehicles

DO NOT remove or bypass the factory negative cable
Your new Big 3 ground wire runs alongside the factory cable
The RVC sensor must remain on the original negative cable

Goal

This allows improved current flow for high-power car audio systems without confusing the charging system, preventing voltage drop and lights dimming while keeping the vehicle happy.

Common Big 3 Upgrade Mistakes to Avoid

Using undersized wire
Poor or painted ground points
Skipping proper cable termination
Not testing voltage and resistance
Incorrect RVC grounding on modern vehicles

Final Thoughts: Is the Big 3 Upgrade Worth It?

Absolutely. The Big 3 upgrade is one of the most effective and affordable ways to improve your vehicle’s electrical system, eliminate voltage drop, stop lights dimming, and protect your car audio investment.

If you plan to push your system harder now—or in the future—the Big 3 upgrade is the foundation that makes everything else work correctly.

Do it once. Do it right.

Written By

Jacob Morris
Electrical Specialist & Co-Owner, Amped Up Car Audio

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