Need help on metal halide ballst issue

Metal halide ballasts are pretty easy...it's the flourescent ballasts that can be tricky as they have more wires and more configurations in which they can be run. The ballast itself should tell you which end is for power and which end the lamp should be connected to. It's usually pretty straightforward. If you've already given it a try and have specific questions, you may want to post pics and maybe we can tell you what to do from them.

--AJ

 

A picture of the label on top would help, but you are likely going to have a fully contained ballast, (ie, transformer, capacitor and pulse start all in one package).  If that is the case, you should have about 5 wires from the ballast.  2 or 3 coming from your 110Vac, (mains power) and 2 going to your socket.  With Metal Halides, the polarity of the socket does not matter.  Either wire can go to the center pin or the outside socket.  On the mains side, you should have black, white, and green.  Black is your load or 'hot' line.  White is your neutral, and green is your ground.  The voltages that you are going to encounter are all within range of a normal wire nut, so just connect up with some wire nuts that are the right size (likely the orange colored ones).  When you use a wire nut, strip off about 1/2 inch of the insulation on each wire, put the two you want to connect next to each other, and twist the wire nut on.  Keep twisting until you twist the wires coming out of the nut a little bit. 
Michael