This installation is for N Scale Atlas MP15 and uses TCS MP-15N Decoder and was performed by TCS
First, remove the shell by pinching it on either side and rocking it back and forth until it slides off.
Next loosen the two frame screws until the original lighting board can be lifted out.
NOTE: In some locomotives it is necessary to trim back the motor pickups to reduce the risk of incidental contact. Highlighted above in red you can see the motor tabs post trimming.
In locomotives where the motor can shift significantly sometimes a small dab of super glue on the track pickup tab (as seen highlighted in red above) to prevent a short between the motor and the frame.
Lastly, install the MP-15N decoder with the same orientation as the original lighting board.
Replace the shell and you are ready to run your locomotive!