The frame requires some very minor modifications that I do using a Dermal rotary tool with cutoff wheel. The small ridges between the light board clips at each end will need to be removed and also a notch needs to be made on the left side frame at the point shown in this photo.
In this photo all of the frame modifications are done. Also shown is the plastic motor saddle with a notch on the top. The notches on the frame and the saddle are needed for the motor wires.
Re-assemble the locomotive mechanism with the orange and gray wires going through the hole on the top of the left side frame and the plastic motor saddle.
Install the CN-GP decoder boards on the frame and connect the yellow, black, and blue wires as directed in the decoder instruction sheet.
Cut the orange and gray wires to the correct length and re-solder to the front board. All wires should lay flat and not overlap on the top of the frame.
Re-install the trucks, contact strips, and fuel tank.
These Atlas GP7's were among the first N scale engines to have lighted number boards with the numbers already in them. Because the LED they used was so dim, this feature was not really noticeable.
With the bright white LED's that come with the CN-GP decoder, this feature can now be fully appreciated as seen in the photo above. You may even find it necessary to mask for paint the inside of the shell at the ends if the light shines through the shell.