How to Do the Big 3 Upgrade: A Step-by-Step Guide

If your headlights dim every time the bass hits, your stereo is asking for more current than the factory wiring can deliver. The Big 3 upgrade fixes the bottleneck with three heavy wires. Here is how we do it in the bay.

• What it is
• Do you need it
• What you need
• 1. Test
• 2. Disconnect
• 3. Make the ends
• 4. Alternator wire
• 5. Battery ground
• 6. Engine ground
• 7. Retest
• Mistakes

What the Big 3 Upgrade Is

Your charging system runs through three main paths: alternator positive to battery positive, battery negative to the body, and the engine block to the body. Factory wires on those paths are sized for a stock car, not a 1,500 watt stereo.

The Big 3 adds a heavy 1/0 wire alongside each one. Current flows easier, voltage stays higher and your amps get the power they are asking for.

Good to knowThe Big 3 does not make your alternator any bigger. It just stops the wiring from wasting what it already makes.

Do You Need It?

Add up the RMS power of every amp in the car. Under 800 watts, stock wiring usually keeps up. From 800 to 1,500 watts the Big 3 is the first upgrade we recommend, especially if your lights dim on bass notes.

Past 1,500 watts, do the Big 3 and add a rear battery. Big builds also need a high-output alternator.

Not sure where you land?Plug your alternator and amp power into our free Power Planner. It shows your current draw and how much battery you need.

What You Need

A Big 3 kit is the easy button. It comes with pre-cut 1/0 cable, lugs and heat shrink so every end fits. If you would rather cut your own, grab about 10 to 15 feet of 1/0 OFC power wire and a bag of ring terminals.

• 1/0 OFC wirePure copper, not CCA.
• Fuse and holderFor wire number 1, close to the battery.
• Lugs and heat shrinkSized for 1/0 and your bolt size.
• Crimper and cutterA hammer crimper works, hydraulic is better.
• Wire brush or sandpaperFor bare metal grounds.
• MultimeterTo test before and after.

• Elite Audio Big 3 Kit, 1/0 OFCShop now →
• T-Spec 1/0 OFC Power WireShop now →
• Limitless 6-Spot Battery TerminalsShop now →
• 16-Ton Hydraulic CrimperShop now →
• 25-Inch Cable CutterShop now →

Step 1 Test Your Voltage First

Before you touch a wrench, take a reading. Start the car, turn on the headlights and the blower, then play music at your normal loud level. Write down the voltage at the battery and at your amp.

Those two numbers are your baseline. You will test the exact same way when you finish.

Step 2 Disconnect the Battery

Shut the car off, pull the key and disconnect the negative battery terminal first. On newer cars, wait a few minutes so the computers go to sleep. Keep the loose cable tucked away so it cannot touch the post while you work.

Step 3 Make Clean Ends

Every Big 3 wire is only as good as its two ends. Strip the jacket back to the depth of the lug, push every strand in, then crimp it hard with the right size die. Finish with heat shrink.

From the bayTug every lug before you install it. If it moves at all, cut it off and crimp a new one. A loose lug gets hot and wastes the whole upgrade.

Step 4 Wire 1: Alternator to Battery Positive

Run 1/0 from the alternator output stud to the battery positive terminal. Keep the factory wire in place and add yours alongside it. Route it away from the exhaust manifold, belts and fan, and zip tie it every foot or so.

Step 5 Wire 2: Battery Negative to Chassis

Run 1/0 from the battery negative terminal to a solid spot on the body or frame. Grind or sand that spot to bare shiny metal, then bolt the lug down tight with a star washer. Paint and rust make bad grounds.

Step 6 Wire 3: Engine Block to Chassis

Your alternator grounds through the engine, so the engine needs a strong path to the body. Run 1/0 from a clean bolt on the engine block or alternator bracket to the chassis. Leave enough slack for the engine to rock on its mounts.

Step 7 Reconnect and Retest

Reconnect the negative terminal, start the car and repeat your Step 1 test at the same volume. You want a higher voltage at the amp and a smaller gap between the battery and the amp. After a week of driving, check that every bolt is still tight and nothing feels hot.

Common Mistakes We See

• Using CCA wire instead of OFC
• No fuse on the alternator wire
• Grounding to paint or rust
• Removing the factory wires
• Bypassing the battery sensor
• Wire too tight to the engine

Free 12 Volt tool

Going Past 1,500 Watts?

The Big 3 is step one. Power Planner tells you how much rear battery you need and how many big wire runs to bring to the back.

Plan My Power

Gear Up for Your Big 3

Everything in this guide is in stock and ready to ship.

Want the deeper science? Read our Big 3 wiring and fusing breakdown. Installing an amp next? Follow our guide on how to install a car amplifier.