Sometimes he allowed the boy to complete a simple task under close supervision.
And sometimes he made the child explain what he thought was happening before touching anything.
One spring afternoon, the tractor refused to start.
The boy was ten.
He and his grandfather had planned to move a small trailer of fencing supplies.
The old man turned the starter.
The engine cranked.
But it did not fire.
He tried once more.
Same result.
Then he stopped.
The boy frowned.
"Is it broken?"
The grandfather smiled faintly.
"Something isn't working."
"Maybe the engine's dead."
The old man raised an eyebrow.
"That's a mighty large conclusion."
The child looked embarrassed.
The grandfather continued.
"What's the first thing we know?"
The boy considered.
"The starter turns it."
"Good."
"So the engine isn't stuck."
"That's one useful observation."
The boy nodded.
The grandfather opened the hood.
They inspected the relevant systems, following the old man's safety procedures.
Eventually, they discovered a loose low-voltage connection in the modified ignition circuit.
The wire had worked free from its terminal.
Without proper electrical supply, the ignition system could not produce the spark needed for combustion.
The grandfather showed the boy the connection.
"See?"
The child stared.
"That's it?"
The old man nodded.
"Sometimes."
He checked the terminal and corrected the fault properly.
Then they closed the hood.
The grandfather ensured the tractor was safely positioned and operating conditions were appropriate.
He started the engine.
The old two-cylinder John Deere coughed.
Caught.
Then settled into its familiar uneven rhythm.
The boy laughed so hard that he nearly fell from the wooden step beside the barn.
His grandfather smiled.
"Sounds pretty dead, doesn't she?"
The child shook his head.
"No!"
The old man rested one hand on the tractor's hood.
"Remember this."
The boy looked up.
His grandfather continued.
"Anybody can say a machine is ruined."
He paused.
"But a good mechanic needs evidence."
The boy nodded.
"And if somebody tells you the engine is destroyed, ask what they tested."
The child looked toward the wiring.
Then smiled.
"I will."
Neither of them knew how important that lesson would become.
Because less than two years later, the same type of ignition connection would be disconnected again.
Only this time, the failure would not be accidental.