Choosing the Right Alternator for Your 1979-1988 GMC P3500
Keep your workhorse P3500 chassis running strong by understanding its charging system and picking the best replacement alternator.
- Before replacing the alternator, always check the battery connections, ground wires, and the alternator's pigtail connector for corrosion or damage.
- For a heavy-duty P3500, especially a motorhome, upgrading to a higher amperage alternator (105A+) is a smart investment for better charging.
- A new alternator from a quality brand like ACDelco, WAI, or Bosch is often a more reliable choice than a cheap, store-brand remanufactured unit.
- Replacement is a simple DIY job for most owners with basic tools, typically taking about an hour.
Is Your GMC P3500 Alternator Failing?
On a 1979-1988 GMC P3500, the electrical system is relatively simple. This means alternator problems are usually easy to spot. If your alternator is going bad, you'll likely notice a few clear warning signs.
Common Symptoms of a Bad Alternator
- Dim or Flickering Lights: Your headlights and dashboard lights may appear dim, flicker, or get brighter as you rev the engine. This is a classic sign the alternator isn't providing consistent voltage.
- Slow or Dead Battery: The alternator recharges the battery. If the alternator fails, the battery won't get recharged, and your truck will eventually fail to start. You might find yourself needing to jump-start it frequently.
- "GEN" or Battery Warning Light: If your dashboard has a battery or generator warning light, it will illuminate if the system detects a charging problem.
- Squealing Noises: A loud squeal from the engine bay, especially when you first start the truck or turn on electrical accessories like headlights, can be caused by a misaligned or worn-out V-belt slipping on the alternator pulley. It can also indicate failing bearings inside the alternator itself.
- Electrical Problems: The radio might cut out, or other electrical accessories may act strangely. This happens when the alternator can't supply enough power to meet the truck's demands.
Check Your Connections First!
Before you buy a new alternator, check your battery cables, ground straps, and the small pigtail connector on the alternator. On these older trucks, a loose, corroded, or broken wire can cause the exact same symptoms as a failed alternator. A bad ground connection between the alternator, engine, and frame is a very common issue.
Choosing the Right Aftermarket Alternator
For a vehicle from this era, you have many good aftermarket options. The debate isn't just about new vs. remanufactured, but also about quality tiers. For a workhorse like the P3500, reliability is key.
New vs. Remanufactured
New aftermarket alternators are built with all-new components. Brands like WAI Global are known for producing 100% new units and sometimes even include a test result sheet in the box. This provides peace of mind, as there are no used parts that could fail.
Remanufactured alternators are original units that have been rebuilt. Worn parts like bearings and brushes are replaced. The quality of a remanufactured part can vary greatly. A unit from a reputable brand like ACDelco or Bosch is generally a safe bet. However, generic, store-brand remanufactured parts are known to have higher failure rates and are often viewed skeptically in owner forums.
Consider an Amperage Upgrade
Many P3500 chassis were used for RVs or delivery vans with extra electrical loads. The original alternators (often a Delco 10si or 12si style) may have had outputs from 63 to 94 amps. Upgrading to a higher-output alternator (e.g., 105 amps or more) is a common and smart modification. This helps the alternator charge the battery more effectively at idle and better supports any added accessories.
Brand Quality Tiers for Your P3500
Not all brands are created equal. Here’s an honest breakdown of the brands available for your truck:
- Premium & OEM-Tier (ACDelco, Bosch, Remy): ACDelco is the original parts brand for GM, making it a natural choice for fit and performance. Bosch is a well-respected German brand known for quality electrical parts. Remy, formerly part of GM, also has a long history of making reliable alternators. You can trust new or professionally remanufactured units from these brands.
- Quality Aftermarket (WAI Global): WAI is well-regarded for making completely new alternators that meet or exceed original specifications. They are a strong choice if you want to avoid the potential risks of a remanufactured part.
- Standard / Economy (BBB Industries, MPA): These brands often specialize in remanufactured parts and serve the budget-friendly end of the market. While they can offer good value, the quality can sometimes be inconsistent compared to premium brands. They are a viable option if budget is the primary concern, but be aware of the trade-offs.
How Much Does a New Alternator Cost for a 1979-1988 GMC P3500?
The cost will depend on the brand, whether it's new or remanufactured, and its amperage output. Installation is a straightforward job for a DIYer or a quick task for a professional mechanic.
| Part / Service | Estimated Cost |
|---|---|
| New Aftermarket Alternator | $47 - $255 |
| Shop Labor | $100 - $200 |
| Total Professional Replacement | $147 - $455 |
Frequently Asked Questions
Can I replace the alternator myself?
Yes, this is a very DIY-friendly job on a P3500. The engine bay usually has plenty of room to work. The process involves disconnecting the battery, loosening the belt tensioner bolt, removing the belt, unbolting the old alternator, swapping it with the new one, and then reversing the steps. You will only need basic hand tools like a socket set and wrenches.
Are there any recalls for the alternator on this truck?
No. Searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls or technical service bulletins (TSBs) specifically related to the alternator for the 1979-1988 GMC P3500. Any issues you encounter are likely due to the age of the components.
Do I need a special alternator for my P3500 motorhome?
You don't need a "special" one, but a higher-amperage model is highly recommended. Motorhomes have extra electrical demands from lights, water pumps, refrigerators, and house batteries. A higher-output alternator will keep both your chassis and house batteries charged more effectively and reduce strain on the charging system.
What is the difference between a 10si and 12si alternator?
The 10si and 12si are two generations of Delco/GM alternators used during this period. They look very similar and are often interchangeable. The 12si is an improved design with better cooling and, more importantly, better charging capability at low engine RPMs (idle). If you have a choice, upgrading from a 10si to a 12si is a worthwhile improvement.
Technical Specifications
Commonly uses a Delco 10si or 12si style alternator. Check for correct amperage (stock is often 63A-94A, upgrades are common), clock position of the electrical connector, and pulley type (typically a single V-belt).
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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 GMC P3500 Alternator Failing?
- Common Symptoms of a Bad Alternator
- Check Your Connections First!
- Choosing the Right Aftermarket Alternator
- New vs. Remanufactured
- Consider an Amperage Upgrade
- Brand Quality Tiers for Your P3500
- How Much Does a New Alternator Cost for a 1979-1988 GMC P3500?
- Frequently Asked Questions
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