What is the ruling on one who touches his wife's genitals without penetration during the daytime in Ramadan?

Your fast is valid as long as there was no penetration and no seminal fluid was discharged. The discharge of pre-seminal fluid (madhiy) does not invalidate the fast, according to the more correct of the two scholarly opinions. It is permissible for a fasting person to caress his wife, kiss her, and engage in foreplay with her if he is confident that he will not discharge seminal fluid or engage in intercourse.