Optimizing Your One- Or Three-Wire Alternator’s Output

Back when the earth was still cooling, automobiles only had a handful of fuses and circuits. The need for high-output charging systems was the least of anyone’s worries. Today’s vehicles, and even those vintage cars and trucks that have been upgraded with fuel injection, electric fans, electronic ignitions, and numerous creature comforts inside the cabin, have become amp-heavy power users that can push a one- or three-wire alternator’s output to the limit. Many times, the charging system requires a high-output alternator such as those offered by Tuff Stuff Performance.

While many may believe the answer to every question is always “more power,” there are times when the alternator’s output is sufficient but the supporting wiring and other components are not up to the task. We’re going to take a look at a few steps to optimize your one- or three-wire alternator’s output, as well as the entire charging system, to make sure everything is working as it should.

Is A One- or Three-Wire Alternator Better?

There has been a lot of debate as to whether a one- or three-wire alternator charging system is best. The reality is that both have come a long way over the years, and the size of the wiring might have more bearing on your charging system’s performance than the number of wires going to your alternator.

The beauty of a modern one-wire alternator is right there in the name. There's only one wire to hook up. But, you need to make sure the alternator housing is grounded properly, which can be a challenge if it is powder-coated or chromed.

Many factory alternators from the classic car era only had 14- to 16-gauge wires, which are not sufficient to handle higher alternator outputs. The wiring alone can’t handle more than the 45 to 60 amps the factory alternators were putting out. Also, these early vehicles used external voltage regulators, so adding a high-output alternator meant a lot of rewiring and upgrading the existing wires to handle more current.

Early one-wire charging system conversions required a short “exciter” wire from the alternator’s battery terminal to the R terminal at the two-wire connector port on the alternator. This wire triggered the charging system to begin doing its job. The downside is that engine RPM needed to reach a level higher than idle speed to excite the alternator. And, on older vehicles, the exciter wire also controlled the “ALT” light.

Tuff Stuff alternators are engineered to fit factory applications and feature built-in circuitry that will keep the battery charged, even at idle. No more blipping the throttle to begin charging! A major benefit to using a high-output Tuff Stuff alternator is that it can be used as either a one-wire alternator or plugged right into a factory-designed three-wire system.

Using a Tuff Stuff alternator in either a one- or three-wire installation requires no extra effort on the part of the end-user. If you want to use it as a one-wire system, connect the charge wire to the battery and alternator, and you’re done. If you wish to use the three-wire design, connect the charge wire, remove the black plug at the two-wire terminal location, and plug in your wiring. It’s that simple. Tuff Stuff does recommend upgrading the charge wire to a larger gauge (smaller number), as the factory wiring might not be capable of carrying the extra amperes without melting.

one- or three-wire charging cable

Those old, factory wires were designed for the early charging system. If you need a higher-output alternator, you need a thicker gauge wire!

Tuff Stuff generally recommends using an 8-gauge wire for its 100-amp alternators and a step up to a 6-gauge charge wire if the battery is in the trunk. Also, a 140-amp unit should use a 6-gauge wire and step up to a 4-gauge when routing to the trunk. When upgrading to the big 200-amp unit, a 4-gauge or 2-gauge wire is recommended.

Proper Charging Requires A Circuit, Not A Slide

The first thing we learn when dealing with batteries is the fact there is a positive (+) and a negative (-) terminal. That illustrates perfectly how current needs to have a complete circuit for your charging system to operate. Unlike a slide, which constantly flows from A to B, your charging system needs a complete circuit to recharge the battery – also known as the ground. Hooking up that one, beefy wire between your new alternator and battery isn’t going to do any good if the alternator and battery aren’t grounded properly.

Today’s alternators are very capable of keeping up with our power-hungry vehicles. Still, many things like powder-coated accessory mounts, painted surfaces, or simply bad grounding keep them from performing as well as they could. To help combat this, Tuff Stuff alternators have an attached tab that can be used for grounding the alternator directly.

proper grounding of alternator

If the block, brackets, and alternator have no paint or powder-coating to hinder metal-to-metal contact, you might be able to get away with the bracket making a sufficient ground connection between the alternator and engine. You can always add a quick ground wire to see if your alternator’s output improves.

Will A High-Output Alternator Damage My Charging System?

We’ve heard it said that high-output charging systems will damage your wiring or charging system components. All the high-amperage, power-consuming stuff added to your vehicle is what is damaging your charging system, not the alternator. A 200-amp alternator isn’t going to overcharge the battery, it only supplies the amperage necessary to keep the proper voltage.

Think of it this way: an electrical component is going to consume the power it needs to operate, and a properly regulated alternator is only going to supply the necessary amperage to keep the battery charged. The problem arises when you stack multiple power-hungry components on a system that was never designed for them. Many times, enthusiasts wrongly assume that a high-output alternator will solve the issue. The higher-performing alternator will supply the amperage needed to keep the battery sufficiently charged, but the wiring harness is not sufficient to handle the additional load.

Checking to see if your charging system is operating properly

To check and see if your charging system is operating as it should, turn on as many electric accessories as possible and check the voltage of the battery.

As we mentioned above, when you increase the number of high-amperage components in your vehicle, you need to make sure the entire system is up to the task. That includes using the proper gauge wire, making sure all connections are secure, and that all grounds are making good contact. If there’s a voltage drop across a wire, that means there is a problem with the wire, the size of the wire is insufficient, or the connection is bad. Any increase in resistance creates heat. Having melted terminals is often a sign of a bad connection, improper wire size for the current used, or faulty ground. Ensure that the entire charging system is capable of handling the load and your high-output one- or three-wire alternator will serve you well for years to come.

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About the author

Andy Bolig

Andy has been intrigued by mechanical things all of his life and enjoys tinkering with cars of all makes and ages. Finding value in style points, he can appreciate cars of all power and performance levels. Andy is an avid railfan and gets his “high” by flying radio-controlled model airplanes when time permits. He keeps his feet firmly grounded by working on his two street rods and his supercharged C4 Corvette. Whether planes, trains, motorcycles, or automobiles, Andy has immersed himself in a world driven by internal combustion.
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