Sometimes, I'm ready to give up on Twitter. It's not that I don't know with an absolute certainty that it can be an extremely effective marketing, branding, and communication tool for car dealers. It's that I can't seem to convince many dealers that it's an extremely effective marketing, branding, and communication tool.
The biggest roadblock is that it's so easy to automate. Between Facebook and blog posts, it's possible to have a robust Twitter presence that's basically "set it and forget it". The problem is that when it's forgotten, it wilts and dies even though content is flowing in through feeds.
Real Twitter users use two things that differentiate themselves from the "bots" on Twitter. They reply to people with @replies which can be easily seen in a 5 second scan of someone's Twitter feed and they use hashtags to either classify their Tweets or insert a bit of personality into them. It is here that you can get the most benefit out of Twitter as a broadcasting tool (though I would argue that it's much better used as a listening tool, but that's an entire other blog post).
Here's a quick video with some basic tips about hashtags, just in case you aren't fully familiar with them.