Alan I replaced the light socket in the dome light with one with two wires, instead of one wire and a grounded socket.
One wire (shouldn't matter which) goes to a fused 12 volts, the other goes to one side of the dome light switch AND to the wire from your door switch. The other side of the dome light switch is wired to ground.
Now my dome light comes on when a door is opened and/or when I flip the switch.
The key is replacing the socket. I used one for a side marker light.
I plan to convert another dome light soon, should I take pictures of the process?