N Scale Atlas GP38-2 with TCS AMD4 - performed by J.M.
First remove the shell be squeezing it on either side and rocking it back and forth until it lifts off. Once that is complete your chassis should look like the one below. Loosen both screws highlighted in red below to free the lighting board and fit the AMD4.
When the lighting board is removed your chassis should look like the one below.
Be sure that the copper motor tabs are properly aligned so they will not touch the frame or each other.If need be wrap the frame in kapton tape to avoid accidental contact. Once the AMD4 has been installed in the locomotive tighten the screws on the sides of the frame and your installation should look like the one below
Alternatively you can slip the motor tabs through the slots in the decoder. This will ensure good motor connection and reduce the risk of shorting against the frame.
Replace the shell and your locomotive is ready to run.