1666 yield monitor & greenstar, possible??

Yes it is possible. I have the gs2 on my 1660. The moisture and mass flow sensors are ones off the 95/9600 series combine I believe. You have to splice the wiring harnes into the feeder switch and header raise switch plus a power sourceYou also have to wire in a JD tachometer and calibrate it. You need this to give greenstar the groundspeed. The GS2 won't read the case ih tachometer. I have mine wired in under the control panel. You may be able to get groundspeed from the gps receiver but I don't know how. You also have to connect to a shaft speed sensor. I hooked to the bottom clean grain auger. I mounted the receiver on the front of the cab. Doesn't sit perfectly level but it works fine. Mount the monitor to the front corner post. Side post isn't stout enough. The mass flow sensor doesn't mount flush to the top of the clean grain elevator. Make sure you cut the hole big enough so grain doesn't get trapped behind the sensor and distort your readings. I had to cut my hole bigger in the middle of the season to stop this. That's all I can think of for now. Let me know if you have any questions. I think you're right to stay with greenstar as I believe it's the best system and easiest to use