...It's possible that could fry the switch if you had it so that the signal wire, when depressed connected to the ground wire since I don't believe that would be fused unless that's the 5a fuse you were talking about before, in which case it would have tripped.
Not necessarily...could have been a 'resistive' short...remember, it is a coil, so maybe only part of it shorted out, but still have a enough resistance to prevent a dead short and blow the fuse...
But I have no real answer or suggestions since I don't have a clear picture of the actual circuit...
A good multimeter might come in handy though...you can do a DC resistance measurement of the relay coil...