Green’s Dictionary of Slang

(US orig. police) drink-driving; a drunk driver.

1967		R. Conot Rivers of Blood 10: Minikus decided that he had a 502—a drunk driver—on his hands.
1981		J. Elllroy Brown’s Requiem 136: There was an easy remedy for the shakes: drink. [...] I decided to leave the car and walk into town—a 502 in a foreign country was all I needed.
1998		Kottonmouth Kings ‘What’s Your Trip’ 🎵 on Royal Highness [album] What you wanna do, get another 502? / You should have eaten some food / Instead of drinkin on an empty stomach.