For an old Yamaha 12 string STRINGS.... Rubbing alcohol or Electrical spray contact cleaner ?

Best not to use either to clean strings, as either would strip out all oil and other stuff that serves to protect them from rust and corrosion. This is true whether or not the strings are on the guitar. If still on the instrument, it would also risk similar problems with the fretboard, which must have at least some "organic" wood protection. Overdone, the strings will rust and corrode twice as fast, and the fingerboard may crack.

Far better to use a decent guitar polish on a microfiber cloth, wrapped around each string (when loose), which will only remove dirt and acquired stuff. I like Martin's, but that's just me. 

Sure, there's lots of work involved with 12-string strings, so many of us put off changing them, which, as often as not is where the money and time is better spent. At best, you can slow it down but you can't fix "dead". 

I would not use either as they can seriously damage the finish of the guitar.

What are you trying to do?