What's wrong if my 1993 ford tempo is draining the battery while I'm driving??

It's possible that your alternator isn't running at its full potential. Most shops can perform an alternator test without having to remove the part. Or if you have access to a volt meter, you can start your car and set the volt meter to the DC (direct current) setting and if it reads between roughly 13.5 and 15 volts, then your alternator is most likely fine and your battery might have a dead cell and not allowing it to receive an actual charge. Hope it helps.

Make sure alt belt is set to proper tightness and not slipping. Could also be a bad diode in alt. Most parts houses will do a complimentary check for you of the charging system and if something is wrong they will find and tell you what it is.