Installation of Digitrax DH140 in a Kato GP35 Diesel HO
Note: These instructions cover the installation of a decoder with wires into a Kato GP35 HO Diesel. Now it is more common to use the DH150A or DH150K plug n play decoder in this particular locomotive. The DH150 installation requires you to remove the light board inside the locomotive and replace it with the decoder. It is a much simpler and cleaner installation than the one described here.
Tools Needed for Decoder Installation You'll need a few simple tools:
1. A soldering iron, preferably temperature controlled.
2. Solder
3. Screwdriver
4. Small diagonal cutters for cutting and stripping small wire
5. Tweezers
Motor Isolation for Kato GP35 Carefully remove the loco's shell and weight.
To isolate the motor, disconnect the brass strips (motor brushes) from the track pick up rails. Bend them out and cut them short enough so that they won't touch the pick up rails.
Decoder Placement The best decoder placement in this loco is at the rear since it will be away from all heat sources inside the loco and there is plenty of room.
Cutting & Soldering the Red & Black Leads
Cut the red and black power pick up leads to length and solder to the track pick ups. Red to the right or engineer's side and black to the left or fireman's side.
Cutting & Soldering the Orange & Gray Leads
Cut the orange and gray motor leads to length and solder in place. Orange to motor + and gray to motor -. If you want to wire your engine for permanent backwards operation you can reverse these leads. You might do this if you always run this engine backwards as part of a consist.
Lamp Board Modification 
Remove the lamp board and cut the trace shown using a Dremel. Then cut to length and solder the white, yellow and blue wires to the lamp board as shown. This will give you constant brightness directional lighting.
Function Leads Since we are not using the green and violet function leads, we clip them short. If you think you will use these in the future you can leave them a little longer and tape the ends so they don't touch anything else.
Reinstalling the Weight Replace the weight and tuck in the wires so they are not pulled loose when you put the shell back on
Finished Installation That's all there is to it! Obviously, there are locos that are more difficult to install decoders in but, with a little practice, you'll be a pro before you know it!
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