Hey Rob - did you have any luck on this problem? Yeah, I'm pretty sure the sensor/sender feeds directly to the instrument cluster on your car as you mentioned, the Milanos have additional circuitry upstream of the sensor to make convert the signal. Actually, it's the same circuitry, just a smarter place for the sensitive electronics!
If you haven't already, I would:
-Verify sensor is getting voltage by checking leads at the sensor.
-Bench test sensor to verify functional.
If those check out, try continuity checks between the sensor wire and instrument cluster. If that works, then the issue might be related to your speedometer display/display. Related question: does your odometer work? It works off the same signal from the speedo sensor, so if your odo works but needle doesn't, it's probably your speedometer/display.