GMC P25 Ignition Switch Guide for 1975-1978 Models
Having trouble starting your GMC P25 or dealing with weird electrical issues? Your ignition switch might be the problem.
- Verify if your P25 has a tilt or non-tilt steering column before ordering, as the parts are different.
- Symptoms like a no-start or stalling engine can point directly to a bad ignition switch, not always the battery or starter.
- Brands like Standard Ignition offer a reliable, mid-level replacement, while economy brands are available for a lower price.
- A burning smell from the steering column is a critical symptom indicating a potential fire hazard that requires immediate attention.
Symptoms of a Failing Ignition Switch
An ignition switch from the 1970s is a mechanical part with electrical contacts that wear out over time. When it starts to fail on your GMC P25, the symptoms can be confusing. They often seem like a battery or starter problem at first.
- No Crank, No Start: You turn the key and get nothing. No clicking from the starter, no sound at all, even though the battery is good.
- Intermittent Starting: Sometimes your truck starts perfectly, and other times it refuses to, with no clear reason.
- Stalling While Driving: The engine can suddenly shut off while you're on the road. This might happen when you hit a bump, which jiggles the worn contacts inside the switch.
- Accessory Power Loss: Your radio, dashboard lights, or heater fan might flicker or stop working altogether. This happens because the switch is failing to send a steady power signal to those circuits.
- Engine Starts, Then Dies: The engine fires up for a second and then immediately shuts down.
- Burning Smell: A plastic burning smell from the steering column area is a serious warning sign. It means the switch is overheating and could be melting wires, creating a fire hazard.
Choosing the Right Aftermarket Ignition Switch
For a vehicle from the mid-1970s, new original equipment (OEM) parts from GM are no longer available. Your only option is the aftermarket, which offers several quality levels.
Pro Tip: Tilt or No Tilt?
The most common ordering mistake is getting the wrong switch for your steering column. GM used different ignition switches for columns with tilt steering versus those without. Always confirm if your P25 has a tilt wheel before ordering a new part.
Brand Quality Tiers
- Standard Ignition (SMP): Standard is a well-known aftermarket brand that has been around for a long time. Their parts are generally considered a reliable, mid-tier option that meets original specifications. While most users find they work well, some online reviews mention occasional quality control issues with parts failing early or not fitting perfectly. For most owners, Standard is a dependable choice.
- Rostra Powertrain: Rostra is known in the aftermarket for various electronic components. While they have a general reputation as a supplier of electronic solutions, specific owner reviews for their ignition switches are not as common. They can be considered a viable alternative if available.
- Replacement (Economy Brands): These are often the most budget-friendly options. They are designed to function correctly and will get your truck running again. However, their long-term durability and the quality of materials may not match that of more established brands. These are a good choice if the budget is the primary concern.
Aftermarket Ignition Switch Cost for 1975-1978 GMC P25
| Brand Tier | Estimated Price |
|---|---|
| Economy (e.g., Replacement) | $20 - $35 |
| Standard (e.g., Standard Ignition, Rostra) | $35 - $56 |
Prices are estimates and can vary based on the retailer and specific part number for your vehicle's configuration (tilt vs. non-tilt).
Frequently Asked Questions (FAQ)
Is the ignition switch the same as the lock cylinder?
No. The lock cylinder is the mechanical part you put your key into. The ignition switch is the electrical part it controls, which is typically mounted further down the steering column and connected by a metal rod.
I replaced the switch but my truck still won't crank. What else could it be?
On these older trucks, the starting circuit is simple. If the switch is new, check the neutral safety switch (for automatic transmissions) or the clutch safety switch (for manual transmissions). A user with a '75 GMC truck found their no-start issue was caused by a loose wire at the clutch switch, not the ignition switch itself. Also, check for power on the large purple wire at the starter solenoid when an assistant turns the key to 'START'.
Are there any recalls for the ignition switch on a '75-'78 P25?
No, searches of the National Highway Traffic Safety Administration (NHTSA) database show no open recalls for the ignition switch on the 1975-1978 GMC P25.
Can I replace the ignition switch myself?
Yes, this is a very feasible DIY job for someone with basic hand tools. It typically involves removing the lower plastic covers on the steering column, unplugging the electrical connectors, and unbolting the switch from the column. You do not need to remove the steering wheel.
Technical Specifications
OEM Part Numbers: 1116616 12339179
Column-mounted electrical switch actuated by a rod. Available in two main versions: one for tilt steering columns and one for non-tilt columns.
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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.