A Guide to Replacing the Alternator on Your 1979-1987 GMC G3500
Keep your classic G-series van powered up and on the road by choosing the right new aftermarket alternator.
- Verify your van's required amperage before buying; upgrade to a high-output unit if you have added electrical accessories.
- Stick with reputable brands like ACDelco, Bosch, or Remy for reliability; a quality remanufactured part is better than a cheap new one.
- The replacement is a straightforward DIY job for many owners, typically taking about an hour with basic tools.
- While replacing, inspect the area above the alternator for oil or coolant leaks, as this is a common cause of failure on G-series vans.
Is Your G3500's Alternator Failing?
For a workhorse like the 1979-1987 GMC G3500, a reliable charging system is critical. The alternator is a common wear-and-tear item, and its failure can leave you stranded. Recognizing the early warning signs can save you from a breakdown.
Common Symptoms of a Bad Alternator
- Dim or Flickering Lights: Headlights and dashboard lights may dim at idle and brighten when you press the gas. This suggests the alternator isn't producing enough power.
- Battery Warning Light: A light on your dashboard shaped like a battery (or labeled 'ALT' or 'GEN') indicates a problem with the charging system.
- Weak or Dead Battery: If you need to jump-start your van frequently, the alternator is likely failing to recharge the battery.
- Whining or Grinding Noises: A high-pitched whine or grinding sound from the engine bay often points to failing bearings inside the alternator.
- Slow Electrical Accessories: Power windows that move slowly or a weak-sounding radio can be caused by insufficient voltage from a failing alternator.
Vehicle-Specific Known Issue
On G-Series vans, the alternator's location can make it vulnerable to fluid leaks from above. A leaking valve cover gasket or heater hose can drip oil or coolant directly into the alternator, causing it to fail prematurely. When replacing your alternator, inspect the area above it for any signs of leaks.
Choosing the Right Aftermarket Alternator
For a vehicle from this era, you don't need to hunt down a rare, expensive OEM part. High-quality aftermarket brands offer excellent performance and reliability. The most important factor is matching the amperage (output) to your van's needs.
Check Your Amperage
G3500 vans came with different alternator outputs depending on the factory options. Standard models might have a 63-amp alternator, while heavy-duty or camper models could have 78-amp, 94-amp, or even higher-output units. If you've added electrical accessories like extra lights, a large stereo, or an inverter, you should consider a high-output alternator from a brand like Powermaster or Proform to handle the extra load. Using an underpowered alternator will lead to premature failure and a weak charging system.
Brand Tiers for Your G3500
- Premium Brands (OEM Quality or Better): ACDelco is the original GM supplier and a top choice for a direct, reliable replacement. Bosch and Remy are also highly respected OE manufacturers known for quality and durability. These are your best bet for a fit-and-forget repair.
- Quality Aftermarket Brands: WAI Global and BBB Industries are well-regarded aftermarket manufacturers. WAI often provides 100% new units that are individually tested, while BBB is a major remanufacturer that often supplies store brands like NAPA. MPA (Motorcar Parts of America) is another large, reputable supplier. These brands offer a great balance of price and performance.
- Performance Brands: Powermaster and Proform specialize in high-output alternators. If your G3500 is a camper conversion or work truck with significant power demands, upgrading to one of these is a smart move.
Pro Tip: Check the 'Clock' Position
When ordering, pay attention to the 'clock position' of the electrical plug on the back of the alternator. Imagine the alternator as a clock face; the plug's position (e.g., 3 o'clock, 9 o'clock) must match your original part for the wiring harness to connect correctly.
Cost of a New Aftermarket Alternator
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket Alternator | $47 - $440 |
| Remanufactured Alternator | $50 - $200 |
| Shop Labor for Installation | $100 - $200 |
Prices vary based on brand and amperage output. Higher-output alternators from performance brands will be at the top end of the price range.
Frequently Asked Questions
Can I replace the alternator myself?
Yes, for most owners with basic mechanical skills and tools. The alternator on a 1979-1987 G3500 is typically mounted on top of the engine and is easy to access. The job involves disconnecting the battery, loosening the drive belt, unplugging two wires, and removing a few bolts.
Should I buy a new or remanufactured alternator?
For this vehicle, a quality remanufactured unit from a top brand like ACDelco, Bosch, or Remy is often just as reliable as a new one. However, many owners prefer to buy a 100% new unit from a brand like WAI Global to avoid potential issues. Avoid the cheapest 'new' no-name parts, as their quality can be questionable.
What tools do I need to replace the alternator?
You will need a basic socket and wrench set (both metric and standard sizes may be needed, like 10mm, 1/2 inch, and 9/16 inch), a pry bar to help with belt tension, and possibly a flat blade screwdriver. Always disconnect the negative battery cable first.
Do I need a high-output alternator?
Only if you have added significant electrical accessories. This includes things like a powerful stereo with amplifiers, extra off-road or work lighting, a power inverter for camping, or other high-draw equipment. For a stock van, the original amperage rating is sufficient.
Technical Specifications
Commonly uses a Delco-Remy 10SI or 12SI style alternator. Available amperages typically range from 63A to over 100A. The 'clock position' of the rear electrical connector and the pulley type (V-belt) must match the original for proper fitment.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- 🛍️ Shop This Part
- Is Your G3500's Alternator Failing?
- Common Symptoms of a Bad Alternator
- Vehicle-Specific Known Issue
- Choosing the Right Aftermarket Alternator
- Check Your Amperage
- Brand Tiers for Your G3500
- Pro Tip: Check the 'Clock' Position
- Cost of a New Aftermarket Alternator
- Frequently Asked Questions
- 🎟️ Get 5% Off