The yellow wire from 87A should go to the green stator wire for the stator brake. But you do not have the yellow wire which means that stator does not have a stator brake. The 2 wires from your stator are DC voltage for charging/running the tractor and the yellow is for the headlight circuit. The bottom line is that if your stator does not have a green wire then the yellow wire from 87A does not connect to anything.
When I said "metered", I was referring to taking ohms readings across various points of the harness to fine out what goes where. There should be 2 relays on this tractor and the 87A of one goes back into the harness and ends up at terminal "L" of the ignition switch. 87A of the other (the one in question) should go to the engine harness and to the green wire of the stator. But you do not have a green wire. Which makes me question if you have the correct stator or not.
If you do not have the green wire on the stator, you should be able to leave the yellow wire from 87A connected to nothing (but taped up on the end) and the tractor should run as normal with no complications.