if you jumper 30 to a door GI light and it doesn't come on, then the wire 20 side has no power, the lamp is burned out, or the lamp socket is bad. If the outer/barrel part of the socket spins easily, you often get a bad connection.
did you check the molex plugs per david post above? Pull the plugs apart and look for burnt pins or pins that are push back in the housing so they don't connect when the plug is put together.