2005-2021 GMC Sierra 1500 V6 4.3L High Output Alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
2005-2021 GMC Sierra 1500 V6 4.3L High Output Alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator
1999-2018-gmc-sierra-1500-4-3l-250-320-370-400amp-high-output-alternator

Fitment:

This is a direct fit high-output alternator for the 2005-2021 GMC Sierra 1500 4.3L. Being a direct fit, this alternator fits directly into your stock alternator location.

Plug:

This high-output alternator comes with a factory style plug so that your OEM plug will plug directly into the alternator. Therefore, with an OEM style regulator, it will have a factory voltage set point.

NOTE: If you require charging at a certain voltage setpoint, we offer a selection of different voltage regulators that you will need to purchase with the alternator for it to be installed. View our Regulator Options Here.

Pulley:

This alternator also comes with a smaller pulley, which causes it to spin faster than a larger pulley. This can help the alternator produce its maximum output. With a smaller pulley, it is required to install a 1/2" - 1" shorter belt. IF YOU HAVE THE ELASTIC BELT SYSTEM PLEASE CALL OR EMAIL CUSTOMER SUPPORT.

See this Blog Article for assistance in finding the correct shorter belt.

Important Belt Type Note: Before ordering or choosing a shorter belt, check whether your factory alternator belt is a stretch-fit belt or uses a tensioner. A stretch-fit system must continue to use a stretch-fit belt, and a tensioner system must continue to use a belt designed for that tensioner. If your alternator uses a stretch-fit belt, contact JS Alternators before ordering to confirm the correct alternator and pulley setup. If you are unsure which belt type you have, contact us for assistance.

Big 3 Wiring:

When Upgrading to a High-Output Alternator, it is required to upgrade your wiring with the Big 3 Wiring Upgrade Kit. It is recommended to use 1/0 100% copper wires for the upgrade. Our Big 3 Wiring Upgrade Kit is 10% off with a purchase of a JS Alternator; use code BIG3DISCOUNT at checkout.

Learn Why The Big 3 Wiring Upgrade Kit is Required for All High Output Alternators

2005-2021 GMC Sierra 1500 V6 4.3L High Output Alternator

$570.00 $712.00

Key Features

  • Direct-fit for 2005-2021 GMC Sierra 1500 V6 4.3L
  • Available in 250A 320A 370A and 400A
  • Factory-style plug with no rewiring
  • Factory voltage set point
  • Smaller pulley for maximum output
  • Requires 1/2" to 1" shorter belt
  • Big 3 wiring upgrade required (10% off)
  • 1 Year Warranty
  • Built in Anderson, SC
Amperage

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Fitment:

This is a direct fit high-output alternator for the 2005-2021 GMC Sierra 1500 4.3L. Being a direct fit, this alternator fits directly into your stock alternator location.

Plug:

This high-output alternator comes with a factory style plug so that your OEM plug will plug directly into the alternator. Therefore, with an OEM style regulator, it will have a factory voltage set point.

NOTE: If you require charging at a certain voltage setpoint, we offer a selection of different voltage regulators that you will need to purchase with the alternator for it to be installed. View our Regulator Options Here.

Pulley:

This alternator also comes with a smaller pulley, which causes it to spin faster than a larger pulley. This can help the alternator produce its maximum output. With a smaller pulley, it is required to install a 1/2" - 1" shorter belt. IF YOU HAVE THE ELASTIC BELT SYSTEM PLEASE CALL OR EMAIL CUSTOMER SUPPORT.

See this Blog Article for assistance in finding the correct shorter belt.

Important Belt Type Note: Before ordering or choosing a shorter belt, check whether your factory alternator belt is a stretch-fit belt or uses a tensioner. A stretch-fit system must continue to use a stretch-fit belt, and a tensioner system must continue to use a belt designed for that tensioner. If your alternator uses a stretch-fit belt, contact JS Alternators before ordering to confirm the correct alternator and pulley setup. If you are unsure which belt type you have, contact us for assistance.

Big 3 Wiring:

When Upgrading to a High-Output Alternator, it is required to upgrade your wiring with the Big 3 Wiring Upgrade Kit. It is recommended to use 1/0 100% copper wires for the upgrade. Our Big 3 Wiring Upgrade Kit is 10% off with a purchase of a JS Alternator; use code BIG3DISCOUNT at checkout.

Learn Why The Big 3 Wiring Upgrade Kit is Required for All High Output Alternators

Shipping is free to the lower 48 states and Washington, D.C. Orders to Alaska and Hawaii are charged a shipping rate, shown at checkout. Orders ship in approximately 3–5 business days, sometimes sooner. Many ship within 1–2 business days. Alternators that require a custom bracket can take 5–8 business days. If for some reason parts are on back order, we will notify you, but this is not common. If an order is placed after 12pm EST, shipping timeframes begin the next business day.

 

REQUIRED Installation Steps: 

(Wear eye protection, remove jewelry/loose items, and allow car to fully cool before starting installation)

 

  • Batteries must be fully charged before installation.
  • Make sure vehicle is off and engine is cool.
  • Disconnect the negative cable from the battery/batteries.
  • Disconnect all other wiring from the alternator.
  • Remove the belt (note the belt routing before removing).
  • Remove the bracket bolts and original alternator.
  • Mount the new alternator. Typically the original bolts will be used.
  • The belt must be replaced with a .5 to 1-inch shorter belt when installing a high output alternator, unless otherwise specified.
  • Install the new belt. Make sure the routing is correct and the belt is aligned with all pulley grooves.

Connections Of Frame/Body: Clean all metal surface of any paint or rust with a wire brush or die grinder. Use a conductive corrosion inhibitor available at any electrical parts supply store.

Grounding (Uni-body frame warning): Many newer vehicles have “uni-body” or sheet metal frame structures with no traditional “full frame”. Because of seams and adhesive attached body components, additional steps may be required for proper chassis grounding. Choose the location on the sub-frame with the thickest metal possible. If there is lower than spec charging voltage at the battery, move ground connections or add additional ground cables to different frame components.

*** WARNING *** Keep all electrical wiring at least 12” away from heat sources to avoid fire of the cable jacket!

There are THREE Regulator styles. Read each to determine which one your alternator has and read its the included notes:

  1. Factory Plug: The factory harness can be plugged into the new regulator. Be sure factory plug is clear of all debris and fully snapped into place in regulator.
  2. Turn On Single Wire Alternators: Follow this step ONLY if we shipped a pigtail plug with your alternator. Connect the excite wire (L) to a 7v to 15v ignition power source and connect the sense wire (S) directly to positive post on alternator. See picture of the Pigtail Plug below. PIGTAIL PLUG:

1987-1990 Jeep Comanche 4.0L High Output Alternator

  1. Self Excite Alternators: Self-exciting or better known as “one wire” alternators will have NO plug on the alternator, and the OEM alternator harness plug will be left disconnected. This type of alternator requires only the positive and negative battery cables to be connected to the alternator to function. These alternators are internally regulated and will turn themselves on and off with engines rotation and regulate their own charging voltage. (This may cause battery light to come on).

Gauges

It is highly recommended you add a dash mounted volt gauge.

  • Connect the battery ground and confirm all other electrical connections are complete.
  • Confirm the belt path is correct and clear of obstacles.
  • Before starting the vehicle confirm that the battery is charged, as starting the vehicle with a discharged battery can damage the alternator.
  • Use a battery charger to charge the battery first if voltage is inadequate.

Ground Path Resistance Test

If resistance is greater than 0.1V confirm the following:

  • Confirm that all paint, anodizing, or rust is removed, and the connections are to bare metal.
  • Make certain all terminals are tight to the wire.
  • Make certain the ground wire is of proper size.

Charge Path Resistance Test

If resistance is greater than 0.1V confirm the following:

  • Make sure alternator charge post nut is tight.
  • Make sure charge wire is proper size.

Battery Recommendation

  • 2000 watts: upgrade main battery, 1 rear battery
  • 3500 watts: upgrade main battery, 1-2 rear batteries
  • 5000 watts: upgrade main battery, 2-3 rear batteries
  • 7500 watts: upgrade main battery, 3-4 rear batteries – 2 alternators
  • 10,000 watts: upgrade main battery, 3-5 rear batteries – 2 alternators

 

js alternators big 3 wiring upgrade kit installation instructions

 

Big 3 Wiring

  • The big 3 Wiring upgrade is an ADDITION to your factory wiring.
  • All factory connections need to remain connected.
  • For protection it is recommended to add an in line fuse to the positive wire.
  • All grounds must be cleaned to bare metal and properly secured.

All factory connections need to remain connected.
For protection it is recommended to add an in line fuse to the positive wire. All grounds must be cleaned to bare metal and properly secured.

Positive 1/0 100% Pure Copper Cable

Connect from the positive stud on the alternator to the positive on the battery

Ground 1/0 100% Pure Copper Cable

Connect from alternator mount bolt to frame/chassis

Ground 1/0 100% Pure Copper Cable

Connect from negative on battery to the frame/chassis

Big 3 Wiring Kit With RVC

  • The big 3 Wiring upgrade is an ADDITION to your factory wiring.
  • All factory connections need to remain connected.
  • For protection it is recommended to add an in line fuse to the positive wire.
  • All grounds must be cleaned to bare metal and properly secured.

All factory connections need to remain connected.
For protection it is recommended to add an in line fuse to the positive wire.
All grounds must be cleaned to bare metal and properly secured.
RVC vehicles have a GROUND SENSOR LOOP in which the ground wire will need to be ran through this loop for proper performance.

Positive 1/0 100% Pure Copper Cable

Connect from the positive stud on the alternator to the positive on the battery

Ground 1/0 100% Pure Copper Cable

Connect from alternator mount bolt through the GROUND SENSOR LOOP to the negative on the battery

Ground 1/0 100% Pure Copper Cable

Connect from negative on battery to the frame/chassis

Depending on the application you may need to run a distribution block for better connections (if you have too many upgraded wires that cannot connect directly to the battery terminals).
UNI-BODY FRAMES: Additional steps may be required for proper grounding, You may need to choose a location on the sub-frame with the thickest metal for grounding.

If you have any questions feel free to email or call us as we are happy to help:

  • questions@js-alternators.com
  • (888) 245-3680

Looking to return an item? Read our return policies and fill out the Return & RGA Requests Form linked here and at the top of our website.

Warranty Information:

All JS Alternators come with a 1 year parts warranty and lifetime labor — we never charge you for our labor to repair your alternator, for as long as you own it. Optional 2 year ($49) and lifetime ($99) warranty upgrades extend the parts coverage period only and do not change the warranty service process. All warranty claims, whether covered by the included 1 year warranty or a purchased 2 year or lifetime warranty, require the alternator to be sent in to JS Alternators for inspection, testing, and repair. Warranty coverage is for repair service only and does not guarantee that a new or replacement alternator will be shipped automatically. Powder coat is non-refundable as it is powder coated to order. Original invoice or copy of original invoice must be included in order to receive warranty service. This warranty covers repairs to the JS Alternator only and does not include other parts on the vehicle. This warranty does not include any labor expenses for installation or uninstallation of the alternator.

The following will void any and all warranties:

  • Improper installation
  • Improper belt length
  • Improper wiring (no installation of big 3 wiring upgrade kit)
  • Changing parts on the alternator, including pulley and regulator
  • Any unauthorized modifications (this includes disassembling the alternator)
  • Painting or powder coating the alternator by an outside party
  • Misuse or abuse of the alternator (not having adequate battery reserve for demand of power draw)
  • If repairs have been completed by anyone other than JS Alternators

This warranty does not cover other parts or equipment on the vehicle and it does not cover labor expenses related to the removal or installation of the alternator, nor rental cars or any other expenses incurred.

SHIPPING POLICY

  • If your alternator arrived defective or was damaged in shipping, we will email you a prepaid return label. An alternator that stops working after it has been installed and used is not considered defective — for those warranty repairs, customers are responsible for shipping the alternator to us.
  • JS Alternators will cover shipping costs of the alternator back to the customer after a warranty repair.
  • Most warranty repairs are completed within 1–3 business days of arrival.
  • Customers outside of the continental US will be responsible for return shipping costs.
  • PLEASE PACKAGE YOUR RETURN CAREFULLY TO AVOID DAMAGE FEES!
  • Costs associated with repairing damage caused by return shipping will be the responsibility of the customer.
  • Expedited, next-day, overnight, and 1-day build/shipping options apply only to eligible JS Alternators-built products. Battery brands and other resale or third-party products are not eligible for expedited, next-day, overnight, or 1-day build/shipping options.

  • If an order is placed after 12pm EST, shipping timeframes begin the next business day.

RETURN POLICY

PLEASE COMPLETE AND SUBMIT THE RGA REQUESTS AND RETURN FORM BEFORE RETURNING ANY PRODUCTS. CUSTOMERS MUST RECEIVE AN EMAIL CONFIRMATION BEFORE RETURNS ARE AUTHORIZED.

All custom ordered alternators, including pulley, regulator, powder coating, and custom housings, are NON-RETURNABLE.

All JS Alternators are custom built to order. New and unused standard alternators may be returned within 90 days of delivery and will be subject to a 10% restocking fee after full inspection. Alternators that have been installed and used are not returnable or refundable. If your alternator arrived defective or was damaged in shipping, we will email you a prepaid return label; for all other returns, you are responsible for return shipping. Exchanges may be available for alternators in new condition that did not work properly for your vehicle. For eligibility, re-casing, non-returnable items and refunds, see our full Return & RGA policy.

Big 3 Kits are NON-RETURNABLE

"Universal" fit Alternators are NON-REFUNDABLE

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Frequently Asked Questions

Shipping is free to the lower 48 states and Washington, D.C. Orders to Alaska and Hawaii are charged a shipping rate, shown at checkout. Orders ship in approximately 3–5 business days, sometimes sooner. Many ship within 1–2 business days. Alternators that require a custom bracket can take 5–8 business days. If for some reason parts are on back order, we will notify you, but this is not common. If an order is placed after 12pm EST, shipping timeframes begin the next business day.

We offer lifetime warranty on alternator labor and a one year warranty on parts. All orders are heavily wrapped for shipping with several layers of big bubble wrap and two layers of boxes along with a Fragile sticker on the box. If you have to ship your alternator back, please be sure you wrap it the same way to prevent further damage. See more details on our warranty page.

Each of our high output alternators come with smaller overdrive pulley. This pulley is made to increase low RPM charging for maximum output. It is custom for the diameter of the overdrive to be less than your factor pulley, depending on the kind of vehicle you own. For this reason, unless otherwise specified, you will need at least a 1/2 inch shorter belt. You can purchase this from any auto parts store. In using the belt and the pulley system, ensure that each part of the pulley system is free of oil or grease, this will help its efficiency.

It is important to make sure that the small regulator plug that is located on the back of the alternator is well plugged in for the correct functionality. Do not forget to plug it in completely, try not to jam the plugs in backwards, and avoid pinching it in order not to create a short. For more information on regulators and wiring see installation instructions.

Our high output alternators come with an overdrive pulley. The pulley is designed to improve low RPM charging so that it yields maximally. Do not change this overdrive pulley out with a larger diameter pulley. When alternator pulley diameter is increased, the output amperage decreases. Changing the pulley will void all warranties

As promised to all our customers, our products are fully tested ensuring their outstanding performance before shipping. In our experience through the years, it is in many cases not the alternator itself. You must ensure you consider a few possible concerns in your troubleshooting – please read the instruction manual thoroughly.

The reason could be one of two things: Either the plug is wired incorrectly or the computer is sensing the higher voltage and causing the battery light to come on even though the alternator is charging properly. Please refer to the instruction manual tab on the website for specific instructions that will help you with wiring. For some older vehicles, the factory style regulator is not available with the hairpin style alternator. This is why your high output alternator will come already “upgraded” with the 15 volt regulator. It will have an oval plug which requires splicing into the factory plug. This is a simple ,fast step and these instructions are detailed for you in the instruction manual.

We currently offer a curated lineup of powder-coating colors displayed on this product page. These are the only finishes available at this time, although we’re always exploring new options for the future. If a new color gets added to the family, you’ll see it show up here first!

We use your vehicles stock voltage unless requested otherwise.

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