Quid, is British informal slang for the pound. Its origins are thought to be from one of two sources.
Either from the Latin quid pro quo meaning "this for that" or from the French quibus meaning "wherewithal".
I could turn the fender question round and ask why the Americans call it a fender? A fender is either a part of a fireplace to stop coals etc from falling out out, a device for pushing things out of the way (like a cow catcher) or a nautical term for something to absorb impact.
I don't know the origin of the word 'wing' on a car. A wing, or fender, evolved from a simple mudguard over a carriage, or early car wheel,possibly the curved shape resembled a wing?? and the name stuck.
Mind you, I had a car once where the wings were so badly rusted they flapped more than a birds wing.