"U" Style, split lighting board locomotive.
The "U" style locomotive frame is characterized by the long strips of metal which rest directly under the decoder on one or both sides of the locomotive. These sections of the frame will make connection with, and sometimes scrape parts off of the decoder.
For this type of frame install the CN Decoder.
To install a decoder in a U simply
remove the section shown in yellow on the left, and make sure it looks like
the image below. Once your locomotive looks like the one below you can pick
"RS" Style installation guide here.