Might well be an allusion to 'wheel' as in to flirt, a measure of sexual success. Like trains entering tunnels, fireworks and popping champagne bottles on screen, engines (especially steam engines) are a metaphor for intercourse.
Being a respectable electrical engineer with a literal mind my dad was oblivious to double meanings. He thought the lyrics of South of the border, down Mexico way were completely innocent. And that Melanie's 'Brand New-key" is a little girl singing about roller skates.
Look closely and you'll find that many – perhaps most – songs are actually about sex. Symbolism, metaphor and tropes aren't a new thing – there was an incident involving Eve, an Apple and the Serpent.
Wheelin' and dealin'
Dave
Edited By SillyOldDuffer on 16/03/2018 11:24:26