Can not say for the Mahindra glow plug controller, but on Ford trucks, that is a sign you have toasted glow plugs.

Testing procedure, unhook the wiring/buss bar from the glow plugs so you can test each individual glow plug.
Test light ground clip on positive battery terminal.
Touch the connector tip of the glow plug with the test light tip.
Light lights, glow plug good
Light does not light, glow plug burnt out.

Second test procedure starts the same as the test light method removing the wires/buss bar.
With an ohm meter you should have about 1 to 1.5 ohms resistance through the glow plug.
The ohm meter test is actually better than the test light, I have seen glow plugs short out internally, which the test light would not show.