Ignition Coil Replacement and Diagnosis for the 1938 GMC T145
Keep your classic GMC's engine firing reliably by understanding its simple but vital ignition coil.
- You must confirm if your truck has the original 6-volt system or a 12-volt conversion before buying a coil.
- A new aftermarket coil from a quality brand like Standard Ignition is more reliable than a used or New Old Stock (NOS) part.
- Symptoms of failure are straightforward and include no-start, stalling when hot, misfiring, and backfiring.
- Replacing the coil is a very simple, low-cost job that any owner can perform in under 30 minutes.
Understanding the Ignition Coil in a Vintage Truck
The ignition system on your 1938 GMC T145 is simple and robust. At its heart is a single, canister-style ignition coil. Unlike modern vehicles with a coil for each spark plug, your truck relies on this one component for the entire engine. When it fails, the whole system goes down. Fortunately, diagnosing and replacing it is one of the easiest jobs you can do on this classic vehicle.
Symptoms of a Failing Ignition Coil
A bad ignition coil on a vintage truck like the T145 will be obvious. You won't have a 'Check Engine' light to guide you, so you'll need to watch for these classic signs:
- No-Start Condition: The engine cranks over but refuses to start. This is the most common symptom of a completely failed coil.
- Stalling When Hot: The truck starts and runs fine, but after the engine warms up, it sputters and dies. After cooling down, it may start again. This points to an internal short in the coil that worsens with heat.
- Rough Running and Misfiring: The engine idles poorly, shakes, or feels down on power. This can happen if the coil is providing a weak or inconsistent spark.
- Engine Backfiring: Loud pops from the exhaust can occur when unburned fuel from a misfire ignites in the hot exhaust system. This is a sign of a serious ignition problem that should be addressed immediately.
Confirm Your Voltage Before Buying
Your 1938 GMC T145 originally came with a 6-volt electrical system. However, many of these trucks have been converted to a more modern 12-volt system over the decades. Installing the wrong voltage coil will cause it to fail quickly or provide a very weak spark. Always confirm if your truck is running a 6-volt or 12-volt system before ordering a new coil.
Choosing the Right Aftermarket Ignition Coil
Original new parts for a 1938 vehicle are no longer manufactured. Your choice is between a modern aftermarket part or a risky used or New Old Stock (NOS) part. For a critical component like the ignition coil, a new aftermarket part from a quality brand is the most reliable option.
Standard Ignition Brand Quality
Standard Motor Products (SMP), the maker of Standard Ignition parts, is a well-regarded brand in the aftermarket. They have a long history of producing ignition components that meet or exceed original specifications. Their products are engineered using modern materials and technology, which often results in a more durable and reliable part than what was available in the 1930s. For a classic truck, a Standard Ignition coil is a dependable choice for keeping it on the road.
A Note on Fitment: Some aftermarket coils may have a slightly different diameter than the original factory part. In some cases, you may need to slightly bend or modify the coil's mounting bracket to ensure a snug fit. This is a minor adjustment that is common when working with vintage vehicles.
Replacement Cost Comparison
Replacing the ignition coil on a T145 is an inexpensive repair. The part itself is affordable, and labor is minimal.
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket (Recommended) | $32 - $39 |
| New OEM | Not Available |
| Used OEM | $10 - $25 (High Risk) |
| Shop Labor | $50 - $100 |
Frequently Asked Questions
Is this a 6-volt or 12-volt part?
The original 1938 GMC T145 used a 6-volt system. You must verify if your truck has been converted to 12 volts before purchasing a coil, as both 6-volt and 12-volt replacement coils are available.
Do I need an external resistor with this coil?
It depends on the specific coil and your system. Some ignition coils are designed for use with an external ballast resistor, while others have an internal resistor. Check the specifications of the coil you are purchasing; often, product descriptions will state if an external resistor is required.
Is Standard Ignition a good brand for my classic truck?
Yes. Standard Motor Products is a reputable manufacturer known for producing reliable ignition components that often incorporate modern improvements over original designs. It is a trusted choice for both daily drivers and classic vehicles.
How do I test my old ignition coil?
The simplest test is to check for spark. Carefully remove a spark plug wire, insert an old spark plug into the end, and hold the metal base of the plug against a metal part of the engine block (away from the carburetor). Have a helper crank the engine. If you see a strong, blue spark, your coil is likely working. If there is no spark or a weak, yellow spark, the coil is likely bad.
Are there any recalls for the 1938 GMC T145 ignition coil?
No. There are no recalls or Technical Service Bulletins (TSBs) on file with the National Highway Traffic Safety Administration (NHTSA) for this component on this vehicle, which is expected given its age.
Technical Specifications
OEM Part Numbers: 1115380 1915427 1910405 362702 1854161 1115141
Canister style, external mount. Must match vehicle's electrical system voltage (6-volt for original, 12-volt for converted).
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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.