I thought that the reason there was glass over the instrument panel (battery gauge, fuel, etc.) to prevent people from manually grabbing the speedometer needle and jamming it well over 100 mph - because accelerating that quickly was almost certainly illegal.
A childhood belief about cars

others believed things like this
- I used to think that the E on a gas gauge meant "enough"...Anon
- I used to think that Legal and Illegal meant the same thing (illegal)— Dhruv
- I used to think when an airplane ran out of fuel, it stayed stuck in the sky.— BoB
- The bus needed coins to run; it would melt them down and use them as fuelAnon
- i believed that the only musical instrument on earth was the piano.hey i was only 6 then!!!— velvetryn
- I thought driving while having to pee was illegal.Anon