Bill, I know it is MTH, but there is a distinction between basic MTH engine with marker, and Premier Engine with Bi-directional markers. The GG-1 with bi-dir markers have a special circuit board to control the polarity. The PS-2 board has special flash coding to control the marker circuit board.
TMCC is easier to do, because of the AC wave form and how the R2LC handles the light output. Atlas and some Lionel engines have LED circuit boards and simple cross wiring to allow a FWD headlight to turn on rear RED markers. It would be easy to allow this to turn on FWD green too.
PS-2/3 is pure DC pulsed to get the correct voltage. Your going to have to create a logic circuit, or do some manual wiring logic to get what your after. That is going to require a lot of wire going between the front of the shell and the rear. If it doesn't have spring light contacts, that will also require extra plugs to get the shell off. G
