1940 Chevrolet KC Brake Light Switch: A Comprehensive Guide
Keep your classic KC safe and visible with a reliable new brake light switch.
- The 1940 KC uses a hydraulic pressure switch, not a mechanical one at the pedal.
- Failure is a critical safety issue. Do not drive if your brake lights are not working.
- A new aftermarket switch from a brand like Standard Ignition is the most practical and reliable option.
- Replacement requires bleeding the brake system, which is a crucial step for safety.
Understanding the Brake Light Switch in Your Classic Truck
The brake light switch in your 1940 Chevrolet KC is a simple but critical part. Its job is to turn on the brake lights when you apply the brakes. For this model year, Chevrolet used a hydraulic switch that senses pressure in the brake fluid. Because of its age and design, this is a common part to fail. The original electrical systems and switches from the 1940s were not built to last forever and can become unreliable over time.
Symptoms of a Failing Brake Light Switch
If you notice any of these issues, your brake light switch is a likely suspect. The system is simple, making the switch a good first place to check for problems.
- Brake Lights Do Not Turn On: This is the most dangerous symptom. The switch has failed and no longer completes the electrical circuit to the lights.
- Brake Lights Stay On Constantly: The switch can also fail in the "on" position. This will keep the brake lights lit, which can drain your battery and confuse drivers behind you.
- Intermittent Brake Lights: If the lights flicker or only work some of the time, the internal contacts of the switch are probably worn out.
- Brake Fluid Leak at the Switch: Because it's part of the hydraulic system, the switch itself can develop a leak. You might see brake fluid seeping from the switch body. This is a serious safety issue that can lead to a loss of braking power and must be addressed immediately.
Pro Tip: How to Test Your Switch
You can perform a simple test to see if the switch is the problem. Locate the two wires on the brake light switch. With the vehicle's power on, carefully disconnect the wires and touch them together. If the brake lights turn on, the switch is bad. If they do not light up, the issue is likely with the bulbs, fuse, or wiring.
Choosing the Right Aftermarket Brake Light Switch
For a vintage truck like the 1940 KC, finding a New Old Stock (NOS) GM part is nearly impossible and would be very expensive if found. A used original part is a major gamble, as it could be just as old and unreliable as the one you are replacing.
The most practical and reliable choice is a new aftermarket switch. The technology is straightforward, and modern manufacturing can produce a quality replacement. Standard Ignition (SMP) is a well-regarded brand that produces a compatible switch for your truck. They are known for using quality materials and testing their products to ensure performance.
A Note on Aftermarket Quality
While new aftermarket switches are the best option, some owners of classic vehicles have reported that modern reproduction pressure switches can sometimes fail prematurely. This is not specific to one brand but is a known issue in the restoration community. Despite this, a new, quality aftermarket switch remains the safest and most accessible solution.
Typical Costs for a 1940 Chevrolet KC Brake Light Switch
| Part Type | Estimated Cost | Notes |
|---|---|---|
| New Aftermarket (Standard Ignition) | $38.97 | This is the most recommended, reliable, and available option. |
| New Old Stock (OEM) | $70 - $150+ | Extremely rare and not necessary for this part. Price is highly variable. |
| Used OEM | $15 - $40 | Not recommended due to age and potential for failure. |
| Shop Labor | $75 - $150 | Includes installation and bleeding the brake system. |
Frequently Asked Questions (FAQ)
Are there any recalls for the 1940 Chevrolet KC brake light switch?
No. The National Highway Traffic Safety Administration (NHTSA), which handles vehicle recalls, was not established until 1970. There are no official recalls or Technical Service Bulletins (TSBs) for vehicles from this era in modern databases.
Is replacing the brake light switch a difficult job?
The replacement itself is not difficult. However, because it is a hydraulic switch, you must bleed the brakes after installing the new part to remove any air from the brake lines. This is a critical safety step. If you are not comfortable bleeding brakes, it is best to have a professional mechanic do the job.
Where is the brake light switch located on my 1940 KC?
It is not on the brake pedal. Look for a small, brass-colored switch with two electrical terminals screwed directly into the master cylinder or into a junction block in the metal brake lines.
Why do my new brake lights not work after replacing the switch?
First, check that you have bled the brakes properly; air in the system can prevent the switch from activating. If the brakes feel firm, check the simple things: the bulbs, the fuse for the brake light circuit, and the ground connection at the tail lights, which can become corroded over time.
Technical Specifications
Hydraulic Pressure Activated, 1/8-NPT thread (verify)
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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.