Whats up with my electrical on my motor?

I have a 75 ford f-250 camper special propane fueled. A couple of weeks ago i was Driving her fine and all was good until lately ive tryed to start it and it wont fire. It will turn over but wont fire. I know there is no spark for starters but what could it be if there is no spark. Must be something to do with my distributor cap im thinking but can anyone give me some pointers. I don't think its my timing because i never screwed around with any of that and its got no spark at all.