On the rear of the A unit and both ends of the B unit, removed the coupler and mounting frame together.
The boards in the A units will have the LED along with a couple of other components. Remove the two that are pointed out in this photo. They were needed for the DC operation of the bright white LED but will not be needed for the decoder function output.
The board from a B unit will not have any components on it at all so this step can be skipped.
I have found the quickest way to isolate all the parts of the board is to cut a notch on each side of the board through the two circuit traces.
This step needs to be done on the boards for both the A and B units.
Here are the lengths I cut the wires to.
Blue, white, gray, yellow = 1"
Orange = 1-3/8"
Red, black = 1-5/8"
Kapton tape is best to use for insulating the frame but does not stick to the frame as well as Scotch tape. I clean any oil off the frame of course, but then I use a layer of Scotch tape first then apply the Kapton tape. It sticks very well to the first layer.
Connect all of the decoder wires as shown in this photo. This can be done either before or after the board is re-installed in the engine. The photo shows an A unit. The B unit won't need the white and blue wires.
Special note on the B units
FT's were run with the B units oriented backwards in relation to their associated A unit and were often draw bared together. This is noticeable by the two sets of ladders, the offset of the wheels and fuel tank, and the dynamic brake vents on the roofs of the ones that had dynamic brakes. The PC board in the Micro Trains FT B unit is oriented in the opposite direction as the A unit. This would have not mattered running DC but with DCC we must have a front and a back end to each locomotive.
This photo showing an A B set with the shells next to a pair of mechanisms shows what is going on. This can be corrected by programming the B unit for reverse operation
CV 29 = 07 for 2 digit address
CV 29 = 27 for 4 digit address