Print out this document. As each step in the installation is completed place a "X" or a check-mark through the bullet. All references to the frame are based on the front being at the top or away from you.
In normal analog (DC) operation, the GP18 receives right track power from the red wires connected to the trucks and the bottom motor brush, and left track power from the blue-green wires connected to the trucks and the top motor brush.
Note: The GP18 does not have a rear headlight. It is suggested the yellow and green decoder wires be cut to 1/2", leaving a length that can be used should the decoder be later installed in another locomotive.
Remove the GP18 shell by separating the handrails from the cab and battery boxes. Be careful with the front ones, as they are held in place by only one tab and are easily broken. Next, slide a knife blade between the battery boxes and the frame and slightly pry apart. Wiggling the cab back-and-forth will allow the cab assembly to pop free, and the battery boxes to separate. The cab slides off vertically.
Pull the short hood up and tip it forward like a car hood. Don't worry about breaking the small tab at the bottom front of the hood, as the cab assembly will hold it together later.
The long hood has one catch on each side and another small rear catch near the platform. Slide your knife between the walkways and the body shell, lifting up once more. Be careful working around and through the handrails. You will see the latches pop free. If the long hood doesn't come free, check to see that all the latches on the sides have released. Sometimes they will re-catch wile you are working on the other side.
Set all parts of the shell aside.
Remove the rear weight and modify per the instructions in the section above.
The short hood area (front of the locomotive) has a weight with wings, which prevents the removal of the walkways. Remove the tape which retains the wires to the trucks and carefully move the wires out of the way, so the solder connection does not break. Then remove the weight. Set aside. The chassis will now separate from the walkways with gentle prying along the inside edge. Look underneath the frame to find the small catches to see where you need to apply pressure. Set the walkway aside with the other parts of the shell.
Unsolder all wires from the two motor brushes.
Replace the modified rear weight on the frame and tape the DN93FX decoder in position on the top of the weight, with the wires pointing towards the front of the locomotive.
Solder the orange decoder wire to the bottom motor brush terminal and the gray decoder wire to the top motor brush terminal.
Solder the red decoder wire to the red wires from the GP18 trucks. Insulate the joint.
Solder the black decoder wire to the blue-green wires from the trucks. Insulate the joint.
Temporarily replace the front weight on the frame, and temporarily replace the headlight in position on the frame.
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Solder the white decoder wire to one of the headlight wires and insulate the joint. Solder the blue decoder wire to the other headlight wire and insulate the joint.
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Using an ohmmeter, check to ensure there are no short circuits between either motor brush and the frame, or one motor brush to the other. Resolve any problems before continuing.
Test the operation of the locomotive on the railroad. Resolve any problems before continuing.
Carefully remove the front weight and reinstall the walkway part of the shell.
Replace the front weight and replace the headlight in position. Dress the headlight wires and the wires from the front truck and tape in position on the weight.
Dress the wires from the rear truck at the rear weight and tape in position.
Dress all decoder wires and secure as necessary with tape. Be sure no tape is placed over any moving parts.
Replace the long hood on the frame.
Replace the short hood on the frame.
Replace the cab and battery boxes on the frame, then attach the handrails to the cab and battery boxes.
Verify the overall integrity of the frame and shell. Reassembly of the DCC-modified locomotive is complete.
Test the operation of the locomotive on the railroad. It should operate just as if no modifications had been made. Resolve any problems.
Place the locomotive on the DCC programming track and set the DCC Command Station to the programming mode.
Program Configuration Variable "CV29" to "06" for 2-digit addressing or "26" for 4-digit addressing then program the decoder to the desired address.
Carry out a final check of the locomotive on the railroad.
Record the decoder CV's and address, and the reporting marks of the locomotive.
The conversion is complete. Enjoy your DCC-equipped locomotive.
