Crystal just went both ways.....no training.

Man those cold January mornings were just wonderful to stay in bed and she knew the pad was ok with me

for her to use.
In the beginning always use a scented pad or take a plain one with outside and rub it into the pee she/he just had. I'd do that for a week and a yorkie should have the idea by then and the scent is not necessary. When they do use it rave about and tell them 'good dog' once in awhile give them a treat (very small) but only if you see them pee.
I must admit the first time I saw Crystal pee on it, I gave her a tiny piece of cheese.......she was so food motivated that I could have asked her to dance a jig.