The Big 3 DIY – Upgrading your cars electrical system on a budget

The Big 3 is a simple upgrade you can do to your cars electrical system to provide much more stable voltage. It won’t necessarily increase peak voltage but it should help keep that voltage more stable during high amperage loads.

What exactly is the Big 3 you ask?

  • Battery Ground to Chassis Wire – This can be pretty small from the factory, upgrading it to 4  gauge or larger 1/0 gauge is a solid upgrade on its own. I would go as large as you can afford, over kill will not hurt.
  • Alternator/Engine Block to Battery Ground Wire – Often times this is just a tiny ground strap from the factory, a 4 gauge or 1/0 gauge wire should be used to replace it, you can even do more than one if you’d like or have a massive system. Some alternators have a grounding point, some do not. If yours does use that point, if it does not just bolt it the closest point to the alternator as possible. You’ll be able to tell based on where the factory wire bolts to.
  • Alternator positive Feed to Battery Positive – This wire is usually 8-10 gauge from the factory, which will suit the needs of your OEM electrical system just fine but anything other than a small stereo upgrade and this wire will choke it. You can leave the OEM wire in place but add another large gauge wire from the positive terminal of the alternator directly to the battery, fusing it is a must. You should put the fuse on the battery end of the cable, as close to the battery as possible. This will protect the wire as well as the battery, should the cable short out for some reason.

Big 4 – Optional

  • You’ll see some people say they did the Big 4. This usually means they added an extra ground from the Alternator grounding point to the chassis. You can use the same point as the Alternator ground to battery ground but instead of going to the battery, you’re going to the chassis instead. This just provides the most possible grounding for the alternator enabling it to provide as much amperage as possible.

You can buy kits for the Big 3 from numerous online vendors or make it yourself. I personally just make it myself. Just measure out the length of each cable you’ll need an purchase about 1-2′ more than that to ensure you have enough. I suggest using OFC wire for this project. OFC = Oxygen Free Copper but if you’re on a budget CCA will suffice, CCA = Copper Coated Aluminum.  You then just cut the pieces you need to the proper lengths and attach terminal ends to the cables with a proper crimping tool or solder them on. You’ll need 6 terminals for the Big 3, a pair for each wire. If you do the Big 4, add another pair of terminals. Depending on the type of fuse holder you buy, you may also need a pair of terminals for that too. Some will have direct connections for the wire and some need terminals to connect, so it entirely depends on the type you buy. If you have upgraded battery terminals that have direct wire connections you will obviously not need terminals for those ends of the cables.

You’ll want to sand down all connections to ensure good contact. You can use 120 grit sandpaper or a small grinding wheel or disk.


Here is a connection point grounded to bare metal, painting it after is a good idea to prevent rust.


Here you can see my OEM engine block ground on the right in this photo. On the left you can see I added a 4 gauge ground which leads to the negative terminal of the battery. This is where the alternator is grounded on my car since it does not have a grounding point.


You can see the extra grounds on my battery here, one runs to the chassis and one to the engine block.

– I will be re-doing all mine with 1/0 gauge cable soon as well as adding an upgraded alternator charge wire. I’ll add more photos at that time.

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