4 wires going to 3 wire 220 outlet, can I make it a 4 wire outlet
So I'm replacing an old electric clothes dryer. The existing outlet has four wires going to it (red black white and bare). The outlet style is a 3 wire outlet NEMA "10-20" like shown here - http://www.stayonline.com/reference-nema-straight-blade.aspx. The red, white, and black are wired to terminals and the bare wire is attached to the metal frame around the receptacle. Can I wire these four wires to a new four wire receptacle for my new dryer? Is there a way to test to make sure they're all hooked up right at the junction box (I have a multimeter)? I'm a little nervous since it wasn't a four wire outlet before that maybe one of the wires isn't hooked up at the junction box or something.
Thanks for any help!