For more detail about how I drill and tap holes in frames to get a secure connection for the decoder input, see the post DZ125 in a Kato F3/7B from January 2011.
After drilling and tapping the holes, I re-assembled the motor, trucks, and frames before continuing.
Tap Plastics to secure decoders, wires, LED's, etc. It sets up faster than the Walthers Goo that I had been using for many years. Here I made a clip from a scrap of brass strip to hold the decoder in place while the E6000 sets. At this point the red and black wires are secured to the frame with short 2-56 screws.
After the E6000 had set, I spliced the red motor wire to the gray decoder wire and the black motor wire to the orange decoder wire covering each splice with 3/64" heat shrink tubing. The white and yellow decoder wires are cut to the desired length and connected to T3 size bright white LED's through 1.5K ohm, 1/8 watt resistors. The blue decoder wire goes first to the front LED and then to the rear LED.
This is a view of the short hood or front end of the engine on the layout. The new LED in its location closer to the end of the frame now gives a bright head light.