One informally educated managed to do something on vehicle (10)
I believe the answer is:
Here is my best explanation:
'one informally educated' is the definition.
'managed to do something on vehicle' is the subsidiary indication.
'managed' becomes 'did' ('do' can mean 'manage' as in 'do without').
'to' says to put letters next to each other.
'do something' becomes 'act' (I've seen this before).
'on' says to put letters next to each other.
'vehicle' becomes 'auto' (auto is a kind of vehicle**).
'did' put next to 'act' is 'didact'.
'didact' put after 'auto' is 'autodidact'.
(Another definition for autodidact that I've seen is "Self-taught person".)