The only way you could get a negative voltage is if the point that you are using to measure the voltage is more negative than what you have your negative meter lead hooked to. Since the only source of a negative voltage is the battery you can't have less negative voltage than that. I have seen weird reading when the meter battery is low. Try another meter or buy a test light they are cheap and all you really want to know is will it light the bulb. Even if you had a -11 volts on the bulb it wouldn't care if current is moving through the filament it will generate heat and light no matter which direction it is going.

Neil
http://community.webshots.com/user/neilhatten