I'll look thru my manual and see if it gives the color codes. Only 3 wires? I figured 4. 2 for the start circuit ans 2 for the back-up lights.
The easiest way is with an ohm meter. Pick one wire and check the other 2 while in park. If you have continuity between 2, then put the shifter in R or Drive. If you lose continuity, then these 2 are the neutral safety wires.