Or of course, possibly a fuse. Start with the simple (and less expensive) options and work your way up. Make sure the fuses are all intact and have good connections, then move to the relays, etc. Also, make sure the wiring harness(es) aren't frayed, worn, or broken anywhere. Could also possibly be a bad ground? Not sure on that one, I would think if that were the case there would be other problems as well.