the license plate is a 1917 New York
the below plate is a 1927 California plate
The driver heard a yell for a taxi, and he reaches up to activate the brake to slow down
below are the many different controls the driver has, you can see he pulls the choke (this was a real thing before advanced carbuerators, it allowed the carb to run better by adjusting the amount of air running through it "Choking" the air supply, creating a vacuum that made the fuel metereing circuit run richer )
and here you can see how the mule power is stopped... they close off the food that mule eats. No food, and the mule stops walking toward it. When the lid is lifted, the food is available, and the mule walks toward it, moving the taxi
the fuel level indicator was a float on the water supply of the mule.
Meanwhile in the engine bay, Farina (the black kid before Buckwheat) is making engine noise by rolling a cam against the "ingine" stick
Here you can see Farina in the engine bay... with a pump, starter, that ingine, and the radio
When they pulled the radio string, Farina started singing, saying he was Tony Wons... I happen to have a donzen books by Tony Wons... and was surprised to hear this. It places the movie from 1929 to 1943 I think, as that is the last year of Tony Wons' scrapbook I have. They are very good
After singing he played the kazoo
You can almost make out the paddle that smacked the mules butt, and made him walk faster. It's hinged at the top of the spare tire pile on his back, at the upper left corner of this photo
Above is the "Fare Master" that indicated how many pennies they were charging to go to a destination