2G alternator charging issue

[Fear]

i recently bought a 96 eclipse gst with some gearbox fix on it. after i got it fixed and started the car the battery charging light on the instrument cluster was lit and also some other light which i don´t know what it is? i measured the voltage on both the batterys + and the alternators + and it was about 12v. since it wasn´t charging i swapped the alternator with the one from my 96 talon tsi awd since i know it´s working properly. when i put the battery terminal on it came some sparks and the 100a fuse in the engine bay blew.
got any ideas what could be the problem?

 

[concept4g63]

Make sure you connected the terminals correctly and make sure everythings co.nected right. No grounded connextions anywhere. Did you disconnect the battery when you swaped the alternator

 

[Fear]

the terminals were connected correctly and i disconnected the battery when i swapped the alternator. i don´t know if everything is connected right since i got the car in the middle of a gearbox change and am pretty new with dsm´s. the thing is when i started the car before the alternator swap the 100a fuse was intact and the charging light was on and so on. why did it blew after the swap?