Ignition Coil Guide for the 1937-1938 GMC T14A
Keep your classic GMC's 6-volt system firing reliably with the correct new ignition coil.
- The 1937-1938 GMC T14A uses a 6-volt electrical system; you must use a 6-volt coil.
- Symptoms of failure include no-start, stalling when hot, and rough running.
- A new aftermarket coil from a brand like Standard Ignition is more reliable than a decades-old used or NOS part.
- Replacement is a simple DIY task that most owners can complete in under 30 minutes.
Is Your Ignition Coil Failing?
For a truck as venerable as the 1937-1938 GMC T14A, the ignition system is simple and robust, but parts do wear out. The ignition coil is a common failure point that can leave you stranded. Because these trucks predate modern computer diagnostics, you won't see a 'Check Engine Light'. Instead, you need to watch for physical symptoms.
Common Symptoms of a Bad Coil:
- No-Start or Hard Starting: A weak or dead coil won't provide enough voltage for a spark, making the engine difficult or impossible to start.
- Engine Stalls, Especially When Hot: As a coil fails, its internal resistance can increase with heat. This can cause the coil to stop working when the engine gets to operating temperature, leading to stalling. After it cools down, it might work again for a short time.
- Misfiring or Running Rough: An inconsistent spark from a failing coil can cause the engine to misfire, buck, or run poorly under acceleration.
- Backfiring: If a cylinder misfires due to a bad coil, unburnt fuel can get into the hot exhaust, causing a loud pop or bang.
Choosing a New Aftermarket Coil
For a 1937-1938 T14A, finding a "New Old Stock" (NOS) OEM part is nearly impossible and often a bad idea. After 80+ years, the internal materials of an old coil can degrade, even if it was never used. A new aftermarket coil is the most reliable and practical choice.
Pro Tip: 6-Volt System is Key
The GMC T14A originally used a 6-volt electrical system. It is absolutely critical to use a 6-volt ignition coil. Installing a 12-volt coil will result in a very weak spark or no spark at all. Conversely, using a 6-volt coil on a vehicle converted to 12 volts will quickly overheat and destroy the coil.
Brand Spotlight: Standard Ignition
Standard Ignition (a brand of Standard Motor Products) is a long-standing and well-respected name in the aftermarket. They have been producing ignition components for decades and are a common, reliable choice for vintage American vehicles. For a standard replacement part on a classic truck like the T14A, a new coil from Standard Ignition is a dependable option that meets original specifications.
Cost of a New Ignition Coil for GMC T14A
| Part Type | Estimated Cost |
|---|---|
| New OEM | Discontinued |
| New Aftermarket (Standard Ignition) | $32 - $39 |
| Used OEM (New Old Stock) | $20 - $50+ (High Risk) |
Warning: External Resistor
Some 6-volt systems use an external ballast resistor, while others do not. Most universal 6-volt coils are designed to be used without an external resistor. Be sure to check if your specific coil requires one; using a resistor when it's not needed will weaken the spark. The coils available from Standard Ignition for this application are typically marked as not requiring an external resistor.
Frequently Asked Questions (FAQ)
Is replacing an ignition coil a DIY job?
Yes, for most owners this is a very simple job. It typically involves disconnecting the battery, removing two small nuts holding the coil bracket, and swapping two low-voltage wires and the main high-tension wire that goes to the distributor. The entire process usually takes less than 30 minutes with basic hand tools.
How do I test my old ignition coil?
While there are multimeter tests for primary and secondary resistance, the easiest test is to check for spark. Carefully remove the main wire from the center of the distributor cap, hold the metal end about 1/4 inch from a metal part of the engine block, and have a helper crank the engine. You should see a bright, blue spark. A weak, yellow spark or no spark points to a bad coil or condenser.
Why is a new aftermarket coil better than a used or NOS one?
The materials inside an ignition coil, including the oil and wire insulation, break down over many decades. A New Old Stock (NOS) part might look perfect, but it can fail quickly once put into service. A new aftermarket part from a reputable brand like Standard Ignition is made with modern materials and is a much more reliable choice.
Do I need to replace the condenser with the coil?
It is highly recommended. The condenser works with the coil to produce a strong spark and also protects the ignition points from burning out. Since it is an inexpensive part and located inside the distributor, it's good practice to replace the points and condenser whenever you are servicing the ignition system.
Technical Specifications
Voltage: 6-Volt, Type: Canister, Primary Connection: 2x Screw Terminals, Secondary Connection: Female (for distributor tower), Resistor: No External Resistor Required.
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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.