The installation is for HO-Scale Athearn GP50. It uses T1 decoder and was performed by Jean Lacroix.
First, grasp the shell of the locomotive on both sides just over the fuel tank and lift out the body. You can slide a jeweller’s screwdriver between the 4 slots in the fuel tank and the body to help you.
Remove the top metal motor clip, the light clip and discard them because we are not going to use it after. The motor will have to be pulled out and you can remove also the plastic clips that hold the motor. The tabs on the copper clip located at the bottom of the motor should be bent back or cut away.
Place electrical tape on the slot on the frame where the motor was sitting. It is important that the bottom of the motor is isolated from the frame; otherwise it will create a short circuit and/or burn your decoder!
The grey and orange wires from the harness of the T1 should be soldered to the top and bottom copper clips of the motor.
Replace the plastic clip and replace the motor where it first was. The black wire should be soldered to the metal tab in the front of the frame. The red one will be soldered on the metal tab on either the front or rear truck. A wire should be soldered between the front and the rear truck to insure good electrical contact.
Next, connect the leds and blue, white and yellow wire as per instructions that came with your T1. You can cut back the green and violet wire and cover their end with heat shrink tubing or liquid tape.
Please note that covering all soldered joints with heat shrink tubing or liquid tape is a must to avoid short circuit.
You are almost done! Just put back the body. The locomotive is now ready to go on the track.