This photo shows MC2 decoder installed. Notice the two yellow capacitors are gone and the MC2 decoder is in there place.  The decoder is held in place with 1/4" wide Capton tape.  The leads were kept just long enough to allow for a very tidy installation.  The solder pads on the light board were tinned. The wires were tinned  Then the wires were soldered to the light board. It is not necessary to pass the wires into the holes in the light board. In this installation they were just soldered flat on the pads.  The pads are numbered starting with 8 on the left then 1,2,4,5,6,7 (three is skipped).  Solder the wires as follows:  8= red, 1= orange, 2= yellow, 3 is not there, 4= black, 5= gray, 6= white, 7= blue.