Well its hard to say. It could be many different things. I'm not the best at electrical issues, but I would start with the simple things.
Battery connections, and the other connections. I had a wire come loose from the back of the key switch once. Check the fuses.
Once your sure that the connections and fuses are good, get your meter and start the search for where the 12 volts stops. I'm sure
one of the guys with more electrical knowledge will chime in soon.