to get the correct ignition unit, consider that there are different models from xt 1990
2KF model only kick
3TB model kick
3TB electric start
The first three letters are in your model number printed on frame, and these letter should be the same first three in your engine number (right side under exhaust).
3TB Kick has CDI unit, 3TB elestart has TCI. So if your bike has the kick is probably the first one, if NOT the second. If has both, please post here, will try to help you further.
Getting the service manual from your model (3TB is in first post of this section) you will find the wiring diagram fro your bike, with all wire colors. As a general rule, ignition unit, coil, stator go together and you cannot mix them from different model. I mean, maybe you can use a coil from cdi model in another cdi (43F-2KF) but you cannot use a cdi coil on a TCI model, it could eventually start but would probably fry your ignition unit in a short term.
Sorry for being so long, but having a bike of unknown origin means that it could have been already mixed up by previous owners.