Oops. You're right, the green power indicator LED is the one at lower left. The middle red LED turns on when the relay is successfully triggered (relay clicks on).
Well, this is quite the pickle!
Above shows my experiment. Again, I don't have a FT turnout and am proposing a method that turns on the relay with +5V DC and turns off the relay with -5V DC. As shown in the photo I was able to reliably trigger the relay with as low as 2.5V DC. And at 5V DC the current required from the yellow wire was only 1.5 mA which I'd think the FT turnout can supply; but this is an assumption.
If you have not abandoned ship (yet),
1. confirm the silver band on the diode is oriented as shown. btw, what diode are you using?
2. disconnect the yellow wire and touch the left side of the diode (without the silver band) to DC+. This applies 12V to the IN trigger and should fire the relay for sure!
3. can you read the white markings on the component I call R5 - should be 3 digits like "222".
4. do you have a voltmeter?