Why do truck drivers in movies honk their horns by pulling on a rope above their heads? Do trucks not have the button to activate the horn inside the steering wheel like normal cars?
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Because it’s attached to the air horn which is located just above the cabin.
They still have a regular horn on the steering wheel, but it’s not as loud.
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The air horn pull is up and out of the way so you don’t activate it accidentally – air horns are loud, can get you in trouble if you blast it certain areas, certain times of days. The truck will have a regular steering wheel “meep” horn like a car, but its not much louder than a car’s.
Also, back in the day, customizing your air horn for your rig was a thing; easier to do when its not mixed up with the steering wheel electrical harness.
Plus: air horn pull = fun.
For a long time trucks and buses and other large vehicles used those lanyards attached to the roof to activate their horns. They just used a different type of horn than cars did and that’s how they worked.
Modern trucks usually just have wheel mounted horns like cars do but a couple still use the lanyards.
They still do it in movies because it’s become a recognizable trope for audiences, just like how swords make that loud “shhhhhiINK” sound when unsheathed (they don’t), or any pistol makes a mechanical cocking sound when being picked up or waved around when most pistols don’t even have hammers anymore.
It’s air horns
Large trucks use compressed air to operate thier brakes because it would be nearly impossible to operate the brakes the way a car does due to the number of wheels and how braking is done on thier trailers.
That means nearly all trucks have a large amount of compressed air stored in tanks ready for use.
The pull chain type horns are a air horn the has a valve that opens when you pull the string. The horns are mounted on the roof on alot of trucks and trains as such the hose with the air runs in the roof. That makes it a easy and cheap spot to put the valve.
With the cheap cost of electrically operated air valves alot of truck designs have moved to a button and relocated the horns to locations behind the bumper.
Some brands like “usually the American brands” have kept the roof horns and chain for brand visual consistency and customer appeal “e.g:look just like the truck your daddy drove”.
The air horn has no electrical activator or switch.
The cord was pulled to mechanically open the valve to let compressed air into the actual horn.
As a kid riding in my parents’ car, used to mimic the cord pulling as we passed a truck to get the trucker to blow his horn.
I love that OP mentions truckers “in movies.” My childhood home was about 300 feet from Route 66. As a boy (@ sixty years ago) it was hugely entertaining to stand near the side of the highway and do the “pulling the horn” gesture at passing trucks. It was so gratifying when they’d honk in reply.
I see you never sat by the side of the road and did the arm motion to get passing trunks to blow their horn.
Edit: “I’m” to “I”
“…in movies honk their horns…”
Maybe it’s just where I live (southern US) but we have a tradition of pretending to pull our own air horns down in a passenger car/truck and then the trucker blows his horn in response.
So, I can’t answer for the push button on a steering wheel. But the horns that they blow in my area are definitely from a pull string.
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