i have a 96 ranger i am told its just a relay most commonly that went but how can i be sure

check out this link.
TRS Magazine - Blower Motor Diagnosis

Locate the Relay, have someone turn the system on with the fan set to medium, while you are near the relay listening you should be able to hear the relay kick over. If it does not and it is a metal relay you can pry the flex locks back and remove the metal cover, then clean the swing arm contacts and then try again. Pleastic ones often have a fitted cover with two tiny cutouts where inner tabs snap into place you can use a tiny screwdriver to dislodge them and pull the plastic cover to do the same. G/L