How do I wire a 4 prong plug into a an old receptacle with only red and black wires with metal conduit into metal box?
Warning: You'll be working around live electrical wires during this procedure. If you don't feel comfortable doing so, please contact a local licensed Electrician.


Okay, going off of what you have, you need at least a 3/4in conduit back to the panel. You are going to need to pull a white and a green from the panel to the receptacle box and install a ground stinger in the metal box to bring it up to code. The wire will need to be sized to the amp draw. If it is not a cost thing I would pull all new wire in using the old wire to pull it in. 

You can turn of the main breaker to the panel, but the feeders from the meter will be hot. 


  Warning: You'll be working around live electrical wires during this procedure. If you don't feel comfortable doing so, please contact a local licensed Electrician.