No wipers or headlights

The problem I'm having is that the windshield wipers, headlights, radio, heater, gauges, electric doors windows and locks keep cutting out all the time. Actually, they spend more time out than they do on. At first I thought with that many things going out all at the same time, it would be a grounding problem. I ran a separate line (ground only) and switch for the headlights and at least got them working. Now I'm really confused! Is it a grounding problem or a relay problem? It just seems to me that that's a lot of things on one curcuit.