The 39-year-old driver had his left leg amputated in 1996 after a gunshot injury, leaving him unable to press the clutch to change gears, the city's traffic department said in a statement.
To keep driving, he sat his son next to him in the driver's seat, telling the boy when to press the clutch for gear changes, chief traffic inspector Merle Lourens told AFP.
The driver, who was not named, had an expired learner's permit, but only to drive automatic vehicles. The truck's licence had expired two years ago, and it had a broken parking brake and a broken seat belt, she added.
He was fined 1,000 rand (£90).
"He won't be allowed to drive, but he shouldn't have been driving in the first place," she said.
