I just popped this into an existing save - I finished the research and put down a vehicle tracker but trains are not revealed. Does it have limited range?

As I recall chunks with vehicles are scanned faster than fog of war settles in.

I somewhat abandoned this mod months ago in favor of Ssilk's Radar Tracker so my memory is a bit hazy.

0.3.0 can be added to exiting games. It will correctly scan all locomotives and vehicles for every force and reveal those matching the placed tracker's force.