The resistor pack is installed in an air duct to cool it, since resistors of that size tend to build up heat. It probably failed the second time because it got too hot. You can get away with testing it first, but it needs to be installed before you run current through it for any length of time.
1997 Oldsmobile Cutlass Supreme SL. 3100 v-6. Auto. 4-door. Green.
2004 Chevrolet Silverado. 5.3 v-8. Auto. 4wd. Long bed. White.