You
cannot lubricate the ball joints on a 1999 Ford Ranger (or most modern vehicles). Unlike older vehicles with grease fittings, the ball joints on a '99 Ranger are sealed units. They're designed to be a maintenance-free component. Attempting to lubricate them will likely damage the seals, leading to premature failure and expensive replacement.
If you suspect a problem with your ball joints (clunking noises, excessive play, etc.), the correct course of action is to have them inspected by a qualified mechanic. They will assess the condition and replace them if necessary. Trying to "lubricate" a sealed ball joint will not fix a problem and will likely worsen the situation.