1951-1954 GMC S370 Brake Light Switch Replacement Guide
Diagnose and replace the faulty brake light switch on your classic GMC S370 to ensure your brake lights work every time.
- Driving without working brake lights is illegal and critically unsafe; replace a faulty switch immediately.
- These trucks likely use a hydraulic pressure switch, which requires bleeding the brakes after replacement.
- Before ordering, visually confirm if your truck has a hydraulic switch on the master cylinder or a mechanical one on the pedal arm.
- Aftermarket brands like Standard Ignition are a reliable and common choice for this repair.
Is Your Brake Light Switch Failing?
A bad brake light switch on a classic truck like the S370 is a major safety issue. Since these vehicles lack modern electronic warnings, you must rely on visual checks. Watch for these common signs of failure.
Symptoms of a Bad Switch
- Brake Lights Don't Turn On: The most obvious and dangerous symptom. The switch is failing to complete the circuit.
- Brake Lights Stay On: The switch can fail in the 'on' position, leaving your brake lights constantly lit. This can drain your battery, confuse other drivers, and burn out your bulbs.
- Intermittent Lights: The lights may flicker or only work when you press the brake pedal extremely hard. This indicates the switch is wearing out internally.
Check Your Switch Type Before Ordering
While most 1951-1954 GMC trucks use a hydraulic pressure switch located on the master cylinder, some GM trucks of this era used a mechanical switch attached to the brake pedal arm under the dash. Before buying a replacement, look at your brake pedal assembly and master cylinder to confirm which type your S370 has. This guide focuses on the more common hydraulic switch.
Choosing the Right Aftermarket Brake Light Switch
For a vehicle over 70 years old, finding original GM parts is nearly impossible. The standard and most reliable choice is a new aftermarket part.
- OEM vs. Aftermarket: New Old Stock (NOS) GM switches are collector's items and not practical for a repair. A used switch is not recommended for such a critical safety component. A quality aftermarket switch from a reputable brand is the best option.
- Available Brands: Standard Ignition (also known as Standard Motor Products or SMP) is a widely available and trusted brand for this part. They have been making quality replacement parts for decades and are a reliable choice for your GMC.
Replacement Cost
Replacing the brake light switch is an affordable repair. The main cost variation comes from whether you do it yourself or hire a shop, as bleeding the brakes is required.
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket (Standard Ignition) | $25.79 |
| Shop Labor | $90 - $150 |
| New OEM | Not Available |
| Used OEM | Varies, but not recommended |
A Note on Installation
Replacing a hydraulic brake light switch requires opening the sealed brake system. This means air will get into the brake lines. After you install the new switch, you must bleed the brakes to remove all air. Failure to do so will result in a soft or non-functional brake pedal, which is extremely dangerous. If you are not experienced with bleeding brakes, have a professional mechanic perform this repair.
Frequently Asked Questions (FAQ)
Where is the brake light switch on my 1951-1954 GMC S370?
It is most likely a hydraulic pressure switch located on the brake master cylinder or a nearby brake line junction block. However, you should always check your specific truck, as some similar models used a mechanical switch connected to the brake pedal arm.
Can I replace the brake light switch myself?
Yes, if you are comfortable working on hydraulic brake systems. While swapping the switch itself is simple, the required step of bleeding the brakes afterward requires specific knowledge and tools to ensure safety.
Are there any recalls for this part?
No. There are no NHTSA recalls for the brake light switch on 1951-1954 GMC trucks. The National Highway Traffic Safety Administration (NHTSA) was formed in 1970, long after these trucks were built, so official recalls are exceptionally rare.
What happens if I don't replace a bad brake light switch?
Driving without functional brake lights is illegal and extremely dangerous. Other drivers will not know you are slowing or stopping, which can easily lead to a rear-end collision. A switch stuck 'on' will drain your battery and confuse other drivers.
Technical Specifications
Switch Type: Hydraulic Pressure | Terminals: 2 | Thread Size: Typically 1/8-27 NPT
We Have This Part in Stock
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.