One-Wire Or Three-Wire Alternator: There’s No Wrong Choice

When our hot rods were new, the limited output of the alternator was enough to sustain the power needed to run the engine with the headlights on. Back then, high-amp stereos, electronic ignitions, and fuel injection were not part of the power draw on the battery. That meant there was no need for high-amp alternators. Let’s face it, the only additional accessory that many of these cars utilized were maybe an additional pair of speakers in the rear deck.


Tuff Stuff’s alternators are available in chrome, Cast PLUS+, polished aluminum, and powdercoated. Amp ratings range from 100 to 160, and include either a single or double V-groove pulley, or a six-groove serpentine pulley. A “Silver Bullet” aluminum pulley cover is also available on select units.

When many of the cars we now consider classic came from the factory, the alternator typically delivered roughly 40 to 60 amperes. Now however, those classic cars are receiving upgrades like high-output ignitions, stereo systems that shatter windows, and add-on electronics that definitely put a serious draw on the stock alternator. That is why the folks at Tuff Stuff have developed alternators for classic cars that will handle the power needs of today’s enthusiasts. According to Frank Hurst, President of Tuff Stuff, “Our One-Wire or OEM compatible unit puts out more amperage than an OEM alternator at low RPM. It has a patented, low cut-in regulator.” This allows the Tuff Stuff alternator to initiate battery charger at a much lower RPM than a converted OEM alternator.

Tuff Stuff's OEM or one-wire alternators are usable in both one-wire and three-wire installations. With a one-wire install, simply connect the charge wire from to alternator battery post (left) to the battery. 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. If you plan to use the factory three-wire installation, install the charge wire to the post, then remove the black plug (right) and connect your factory two-wire connector.

Adequate Amperes

An alternator’s only job is to recharge the battery. As lights and other accessories draw current from the battery, energy is replenished by the alternator. To keep the battery fully charged, the alternator must provide more amperes than the accessory load on the battery. A common myth is that a higher amperes-output alternator can hurt the battery. That is not true. If the voltage regulator is properly functioning, it will safely keep the battery fully charged and ready for use.

To figure out what amperes output you should use, simply add up the amperes usage of everything in the vehicle. That includes headlights and tail lights, electric fuel and water pumps, and high-power stereo systems. Once you determine your total vehicle amperage draw, add an additional 10-percent just to be safe, and use that number as the minimum amperes output for your application.

Our One-Wire or OEM compatible unit puts out more amperage than an OEM alternator at low RPM. – Frank Hurst

The most frequently asked question when considering an alternator upgrade, is, “should I use a one-wire or three-wire style”? There is no easy answer, as both styles have come a long way in regard to the technology they incorporate.


Upgrading the charge wire is highly recommended, as the factory wiring might not be up to snuff with the new, high-output alternator. Tuff Stuff has dedicated charge wires that are large enough to carry the amperes, and have high-quality, crimped-on brass connectors. Tuff Stuff recommends an 8-gauge wire for its 100-amp alternators, and a step up to a 6-gauge wire if the battery is in the trunk. A 140-amp unit should use a 6-gauge wire, and 4-gauge to the trunk. All 200-amp units should have a 4-gauge wire and a 2-gauge to the trunk.

If you are starting a project from scratch or you want to minimize the amount of wires in your engine bay, a one-wire alternator will simplify the installation. The only drawback to using a one-wire alternator in GM vehicles has to do with the ALT warning lamp (idiot light) on the dash. A one-wire alternator doesn’t use the two-wire connector which supplies electrical current to facilitate use of the idiot light. The two-wire connector houses the exciter wire, which is responsible for turning off the in-dash light.


With the chrome, cast PLUS+, and powdercoated units, you might need to clean the threads with a thread chaser or tap before installation, as these coatings could interfere with the threads.

This is not usually an issue, as most enthusiasts prefer using a volt gauge to monitor charging. However, Tuff Stuff alternators like the 7127, 7139, and 7140 series can be wired to turn off a warning light. To wire a warning light using one of these battery chargers, simply remove the black terminal plug on the housing and connect the R terminal to the warning-light wire.


Without a good ground, no alternator will properly charge a battery. Tuff Stuff units have an attached tab that can be used for grounding. If the block, brackets, and alternator have no paint or powdercoating to hinder metal-to-metal contact, you might be able to get away with the bracket making the ground connection between the alternator and engine.

Before a dedicated one-wire alternator was developed, enthusiasts would make a jumper wire to “excite” the charging properties of the alternator. This entailed running a wire from the battery post on the alternator to the R terminal at the two-wire plug location. Years ago, the enthusiast-created one-wire system required engine RPM to be at a level higher than idle to start the charge process. This required a quick blip of the throttle. That is no longer the case. Tuff Stuff one-wire alternators utilize internal components that will keep the battery charged, even at idle. “There is no need to worry about using under-drive pulleys or an ignition-regulator turn on with the use of a Tuff Stuff one-wire alternator,” said Mike Stasko of Tuff Stuff.

But, what sets the Tuff Stuff alternator apart from others, is the fact it can be used as a one-wire or a factory-designed three-wire system. Using the alternator in either instance requires no extra effort on the part of the end user. If you want to use it as a one wire, connect the charge wire to the battery and alternator and you’re done. If you wish to use the three-wire system, connect the charge wire, remove the black plug at the two-wire terminal location and plug in your wiring. It’s that simple.

But Wait, There’s More

One thing that many enthusiasts forget to consider, is the increased output of a new alternator. Automotive charging systems use a charge wire that runs from the alternator to the battery. In stock applications, this wire usually is between 10 and 12-gauge. If you’re upgrading the output size of your alternator, it is also highly recommended that you also upgrade the charge wire to prevent a meltdown.

Another issue that can cause a person to pull their hair out, has to do with proper grounding. In order for an alternator to properly charge, it must be properly grounded. Many times, an alternator is attached to a freshly painted engine, and if the paint inhibits grounding, the alternator will not charge. That is why many Tuff Stuff alternators include a grounding tab that should be used to ground the alternator.

Accessory Amp Draw

  • Brake lights 3 to 7
  • Driving lights 4 to 10
  • Electric cooling fan 8 to 20
  • Electric fuel pump 10 to 20
  • Headlights – pair 6 to 20
  • Ignition system 6 to 11
  • Instrument lights 3 to 4
  • Radio 3 to 8
  • Stereo amplifier 10
  • Turn signals 4 to 8
Installing an alternator is a relatively easy task, and one that can be accomplished in your driveway with simple tools. But was upgrading to a new Tuff Stuff 100-amp alternator worth the hour spent wrenching? Any time you can make an upgrade to your classic, it’s worth the time spent.


The C10’s battery is in the stock location, and instead of trusting the 10-gauge factory charge wire, I upgraded to the Tuff Stuff 8-gauge wire just be safe.

Was It Worth It

In this case, the alternator definitely made a difference in the charging characteristics of my C10. For instance, while the volt gauge still displays the proper voltage, when driving the truck, the headlights no longer blink when using the turn signals at night. Also, before the upgrade, I could watch the volt gauge move when operating accessories like the wipers or turn signals. That no longer occurs.

Installing a Tuff Stuff alternator was an easy fix to resolve an inadequate charging issue I had on the C10. The only thing I can say is, I should’ve done it sooner.

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About the author

Randy Bolig

Randy Bolig has been working on cars, and involved in the hobby ever since he bought his first car when he was only 14 years old. His passion got him noticed by many locals, and he began to help them with their own vehicles.
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