Good points already mentioned above.
One more likely problem is the key switch.
Your brake light bulb always gets Voltage, because it always has to work.
All of the other lights depend on the position of your key in the switch....you can have the ignition on, and no lights, in one position of the key.
Or, turn the key one more spot and the ignition and all other lights come on.
The key switch is somewhat of a hassle to get to, but it may have failed, or the connections are crappy.
Pull the plastic wire terminal off of the back of the key switch and shine up the terminals (once you get stuff out of the way to access it)
It may be as simple as that.