Anything with a standard DIN chassis fits in the top slot. It is a tight fit for wiring - wrap everything up carefully so it doesnt' short out against the wiper linkage (common problem!- ask me how I know!).
The "2 inch white module" you're talking about is a fuse holder. It should push in, turn and pop apart to expose the fuse. If there's not one in there, try a 10-amp fuse or whatever Sony recommends. This line is probably the hot wire you need. You really should have a test light or better yet, a multi-meter to measure voltage at these wires. It's essential to have a good solid ground. Crimp on a nice fat terminal lug and attach it to a bare metal grounding point in the dashboard somewhere. If you can't find power in the harness, you can run a wire right over to the fuse block in the kick panel.
You've probably got a (yellow?) wire for a power antenna- you can ignore this and tape it up if you have no power antenna (most 240's don't).
The Haynes manual has wiring diagrams for your year and model.
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Rob Bareiss, New London, CT 86 244, 87 244, 88 744