Thanks for your comments. I know my information is sketchy, but I haven't really had time to crawl around the engine room yet and I am a total ignoramous when it comes to electrical systems. Are you saying that every device should have a wire that goes back to the negative terminal on the battery (or, more likely the bus on the fuse panel)? I always thought that a ground could be, for example, to an engine block. I probably need to do some reading.