Don't know if I've done a FA1, but, the procedure should be much the same.
0 - Disassemble the loco, take photos as you go if this is your first venture into one of these beasts. (should be obvious but...)
1 - Remove the portion of the right rear frame that fits over the left frame. To open up room for the decoder (I used a DZ123 & DZ121 & DZ125 in a FA2, C liner, E8 & ? but the new DZ126T looks like a better option.)
2 - Cut the tracings on the light board between the contact pad and the resistor/led.
3 - Optional file a 45degree bevel on the edge of the frame to allow more room for wires over the motor.
4 - Carefully remove the brush caps from the motor, I found that pulling these off with the motor in a plastic bag keeps the spring & brush from going into orbit.
5 - Solder the orange and gray wires to the caps and reinstall brush-spring-cap.
6 - Solder the red and black wires to the contact pads on the front light board (no rear board on the cab units)
7 - Solder the blue and white wires to the front light board.
I will try to get photos of one of my units tonight. This is a fairly "easy" hard wire installation no special tools needed (soldering iron, hacksaw, and mill file)
