my '97 f150 turn signal works but the flashers won't flash. When the flashers are engaged they do not illuminate.:

 

flashers as in Hazards ?

Some times the hazard contacts get dirty from lack of use.

A few threads report that cycling the hazard button a few times will clean them off.

If this does not work, time to remove the MFS ( MultiFunction Switch ) and test them prior to replacing it.