1966-1967 GMC LI3500 Voltage Regulator Replacement and Diagnosis
Keep your classic GMC's charging system reliable by understanding and replacing your voltage regulator.
- The voltage regulator on your 1966-1967 GMC LI3500 is an external part, making it easy to access and replace.
- Symptoms of failure include dimming/brightening lights, battery issues, and poor engine performance.
- Driving with a bad regulator is not advised as it can leave you stranded or damage other electrical parts.
- Standard Ignition is a readily available aftermarket brand for this application; new OEM parts are not a practical option.
Symptoms of a Failing Voltage Regulator
A bad voltage regulator on your GMC LI3500 can cause a range of electrical problems. Because this part controls the charging system's output, failure can lead to either too much or too little voltage. Catching these signs early can prevent damage to your battery and other electronics.
Common Failure Symptoms:
- Dimming or Flickering Lights: Headlights and dash lights may dim, flicker, or pulse, especially as engine RPM changes. They might also get excessively bright if the system is overcharging.
- Battery Problems: A frequent need for jump-starts or a battery that won't hold a charge points to an undercharging issue. Conversely, a battery that smells like rotten eggs, feels hot, or has a swollen case is a sign of dangerous overcharging.
- Engine Stalling or Performance Issues: The ignition system relies on steady voltage. Fluctuations can cause the engine to run poorly, stall, or even fail to shut off when you turn the key.
- Warning Lights: A "GEN" or "ALT" light on your dashboard is a direct indicator of a charging system problem.
Choosing an Aftermarket Voltage Regulator
For a vintage truck like the 1966-1967 LI3500, finding a New Old Stock (NOS) or OEM voltage regulator is nearly impossible. The good news is that the aftermarket provides reliable, modern replacements. These trucks used a common external regulator design, making compatible parts available.
OEM vs. Aftermarket: While an original Delco-Remy part would be ideal for a concours restoration, a quality aftermarket part from a reputable brand like Standard Ignition is a practical and reliable choice for a working truck. These modern replacements often use updated internal electronics compared to the original mechanical points-style regulators, offering improved reliability. Many owners of similar-era GM trucks have successfully used aftermarket replacements.
Pro Tip: When replacing the regulator, it's a great time to inspect the wiring connectors for corrosion or damage. A poor connection can mimic the symptoms of a bad regulator. Also, ensure the regulator has a clean, solid ground to the chassis, as this is crucial for its operation.
Estimated Replacement Costs
The cost to replace a voltage regulator on this truck is very reasonable, especially if you do the work yourself. The part itself is affordable, and the job requires only basic tools.
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket (Standard Ignition) | $93.90 |
| Shop Labor | $60 - $120 |
| Total Estimated Cost | $153.90 - $213.90 |
Cost estimates are based on national averages and may vary by location and supplier. New OEM parts are generally not available for this model year.
Frequently Asked Questions (FAQ)
Can I drive my truck with a bad voltage regulator?
It is not recommended. If the regulator is undercharging, the battery will eventually die, leaving you stranded. If it's overcharging, you risk permanently damaging the battery, wiring, and other electrical components.
Where is the voltage regulator located on a 1966-1967 GMC truck?
On GM trucks from this era, the external voltage regulator is typically mounted on the driver's side of the radiator core support or on the firewall. It's a small, rectangular metal box with a wiring harness plugged into it.
Is this a difficult part to replace myself?
No, this is a very DIY-friendly job. It usually involves unplugging the wiring connector, removing two or three mounting screws, and swapping the part. The entire process should take less than an hour with basic hand tools.
Do I need to polarize the generator after replacing the regulator?
If your truck is equipped with a generator instead of an alternator, yes. After installing a new voltage regulator, you must polarize the generator before starting the engine to ensure it charges correctly. This is done by briefly jumping the "BATT" and "ARM" terminals on the regulator.
Are there any recalls for the 1966-1967 GMC LI3500?
No active recalls related to the voltage regulator or charging system were found for the 1966-1967 GMC LI3500. A search of the NHTSA database did not show any relevant recalls for this specific model and component.
Technical Specifications
System Voltage: 12V, Type: External, Terminal Count: 4
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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.