I think you should swap the connections at the gate man for the 2 wires that are successfully feeding the light.
Simplistically, the internals for the gateman look like this:
Pay no attention to the letters themselves, but look at the connections I drew. (I forget how Lionel labels them, but the chances I matched exactly what it says on the plastic or in the manual is not too good 
)
C should be the connection to the transformer "hot" (which provides the "hot" for both the light and the "man" - all the time).
B would be a connection (always connected) to transformer "Common". So the light will always light, but B is not connected to the "man".
A is your "Trigger", which is supposed to go to the insulated rail (which then completes the circuit to "common" when a train goes over a properly insulated outer rail).
The fact that you are getting motion when you hook the "Trigger" to the "hot" (center rail) tells me the "common" is already connected to the other terminal of the "man". If it was not, you would just be creating the same voltage on both terminals of the "man" instead of getting the motion (which happens when you have hot on one terminal and common on the other). What you describe how the behavior flips when you reverse the wiring to the track also supports this theory, I believe.
So I think you have currently got C hooked to "common" on your transformer, and B hooked to "hot". That's why when you hook A to hot (via the track center rail) the figure moves.
Swap connections B and C and you should get the motion when you hook the trigger to the outer rail.
The issue with the FasTrack insulated and Isolated sections is I think covered above, but the part I describe above is independent of that. You can solve that part of the problem most likely, then worry about either fixing your gap in the outer rail or getting the needed FasTrack piece to provide the gap.
-Dave
