There are many diesel locos that have been fitted with GPS. It's part of a system called REMMLOT (Remote Monitoring and Management of
Locomotives and Train). This system uses a GPS and communicates important parameters like loco location, speed, fuel levels etc to a central server. Through this system, the control center can communicate with the Loco pilot throughout the trip and guide him through any issues. Most of the diesel locos from Golden Rock (GOC) shed have this. I'm not sure as to which other locos have this system.
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more... Many electric locos (mostly 3 phasers ) have been fitted with RDS ( Remote diagnostic system). I think this system also incorporates GPS ( open to correction).