What the turn signal cancelling cam does
The turn signal cancelling cam is a small rotating part inside your steering column that automatically shuts off your turn signal when you complete a turn. On a 1966 Chevrolet C10, this cam sits beneath the steering wheel and works with the turn signal lever to reset the signal without you having to reach up and flip the lever back manually.
When you turn the steering wheel, the cam rotates along with it. Once you straighten the wheels back out, the cam's shape pushes an internal spring-loaded contact back to the off position, cutting power to the blinking light. Without this mechanism, you would have to remember to switch the signal off yourself — a feature that became standard on most vehicles by the 1960s.
Key Takeaways
- The cancelling cam is a rotating part inside the steering column that automatically turns off your turn signal when you straighten the wheel.
- The cam works by using its shape to push a spring-loaded contact back to the neutral position as the steering wheel returns to center.
- On a 1966 C10, the cam is part of the turn signal switch assembly and rotates with the steering shaft.
- If your turn signal does not cancel automatically, the cam may be worn, the spring may be weak, or the switch assembly may need replacement.
How the cam connects to the steering wheel
The cancelling cam is mounted on the steering column shaft, directly below where the steering wheel attaches. As you turn the wheel left or right, the shaft rotates, and the cam rotates with it. The cam is not a separate part you can adjust — it is built into the turn signal switch assembly.
The turn signal lever on your steering column connects to a contact arm inside the switch. When you push the lever up or down to signal a turn, you are moving that contact arm, which completes an electrical circuit and lights up the turn signal bulbs. At the same time, the steering shaft begins to rotate because you are turning the wheel.
The shape of the cam and how it resets the signal
The cancelling cam has an off-center, rounded shape — not a perfect circle. This shape is the key to how it works. As the steering wheel returns to center after your turn, the cam's edge gradually pushes against a spring-loaded contact arm inside the switch assembly.
When the wheel is fully straightened, the cam's shape has pushed the contact arm far enough that it snaps back to the neutral position, breaking the electrical circuit. This is why the turn signal blinks off automatically. The spring provides the force that holds the contact in the off position until you turn the wheel again.
Why the cancelling cam can fail or wear out
The cancelling cam on a 1966 C10 is made of plastic or soft metal and rotates thousands of times over the life of the truck. After many years and many turns, the cam's edge can become worn smooth, rounded, or cracked. When this happens, it no longer pushes the contact arm far enough to trigger the reset.
The spring that holds the contact in the off position can also weaken or lose tension over time. If the spring is weak, even a properly shaped cam may not push the contact far enough to stay in the off position. In either case, your turn signal will stay on after you complete the turn and will not cancel automatically.
Moisture and corrosion inside the steering column can also damage the cam or the contact surfaces it pushes against. If the switch assembly has been exposed to water or salt, the internal parts may corrode and stick, preventing the cam from doing its job.
Signs that your cancelling cam needs attention
The most obvious sign is that your turn signal does not turn off when you straighten the wheel. You have to manually flip the lever back to the off position every time you signal a turn. This is the primary symptom of a worn or damaged cam.
You might also notice that the turn signal cancels only sometimes, or only when you turn the wheel a certain way. This usually means the cam is partially worn — it works in some positions but not others. Another sign is a clicking sound from inside the steering column when you turn the wheel, which can indicate the cam is cracked or the contact arm is catching on a rough edge.
How to replace the turn signal switch assembly
Replacing the cancelling cam means replacing the entire turn signal switch assembly, because the cam is not sold as a separate part. The switch assembly is located inside the steering column, below the steering wheel.
The job requires removing the steering wheel, the horn pad, and the turn signal lever. You will then need to disconnect the wiring harness and remove the switch assembly from the column. A new assembly slides back in and reconnects to the same wiring. On a 1966 C10, this is a job that typically takes one to two hours if you are comfortable working inside the steering column, or you can take it to a mechanic who works on classic trucks.
Replacement assemblies are available from classic Chevrolet suppliers and are not expensive, but labor costs will depend on your mechanic's rate. If you are doing the work yourself, you will need a steering wheel puller to remove the wheel safely without damaging it.
Frequently Asked Questions
Can I just replace the cam without replacing the whole switch?
No. The cam is molded or pressed into the switch assembly and is not designed to be removed and replaced separately. You must replace the entire turn signal switch assembly. This is actually simpler than trying to disassemble the switch, which can damage the internal contacts.
What if my turn signal cancels sometimes but not always?
This usually means the cam is partially worn or the spring is weak. Sometimes it has just enough shape or spring tension to work, and sometimes it does not. The fix is still to replace the switch assembly. Trying to adjust or repair the internal parts usually causes more damage.
Is a worn cancelling cam dangerous?
It is not a safety emergency, but it is annoying and can confuse other drivers if your signal stays on longer than intended. More importantly, a faulty switch assembly can sometimes cause the turn signal to stay on and drain your battery, or to fail to light up when you need it. Replace it when you notice the problem.
Do I need to remove the steering wheel to replace the switch?
Yes, on a 1966 C10 you will need to remove the steering wheel to access the switch assembly inside the column. You will also need to remove the horn pad and the turn signal lever. A steering wheel puller is the right tool for this job — do not try to pry or hammer the wheel off.
Where can I find a replacement switch assembly for a 1966 C10?
Classic Chevrolet suppliers, online parts retailers that specialize in vintage trucks, and some general automotive parts stores carry turn signal switch assemblies for 1966 C10s. Make sure you order the correct assembly for your truck's year and model, as the design changed over time.