Signal BitSwitch"™ $19.95

This circuit will power a stand alone signal.
Power input can be 10-16V DCC, DC or DCC
Output voltage to the signal = Input voltage
If reduced voltage is need insert
a resistor to the signal common

If you wish to have the signal activate as
as the engine enters the control section
and the signal restore after the last car
exits the control section offset the triggers
as shown below and install offset magnets
on the engine and the last car of the unit

This is easiest to accomplish with HO
 and larger scale equipment as only
the triggers on one side can be pulsed