IMD4 Decoder Installation for Drop-In 
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The upper picture shows the Intermountain SD40T-2 Snoot Nose with its shell on.

This picture shows the locomotive's chassis with its shell taken off and the original lighting board.

Be careful as you take off the shell because it is difficult to remove and can be broken easily.

Gently, unsnap the fuel tank as shown in the picture above.

Using philips screw driver remove the rear screw ( circled in red)

Using philips screw driver remove the front screw ( circled in red)

Once you removed both screws, gently unsnap both locomotive's trucks.

Gently spread both sides of the chassis apart as shown in the picture above and remove the original light board.

Insert the TCS IMD4 decoder so that both motor tabs underneath of the decoder board are lined up with copper perforation of the decoder.

Put the frame back together and make sure all four copper tabs ( circled in red ) of the decoder make electrical connection with the chassis.

Place both trucks back, screw the chassis down with two screws, reassemble the fuel tank and place some Kapton tape on the chassis so that it is isolated from the LED's legs.

Here is the picture of the SD40T-2 Snoot Nose's chassis with the TCS IMD4 decoder installed and isolated LED. Place the shell back on being very careful not to brake anything.