2000 Jimmy- motor Mount/ Electric Problem

I have a brooken Engine mount on my 2000 gmc Jimmy, when i torque the brakes, the engine lifts out of the car on the torque side of the engine and rubbs against the fan shroud and is eating it up! Is this a serious problem that when the gas is pressed the engine lifts up slightly? Could this affect horsepower the engine puts out or the gas mileage? Is this something that i should immediately replace?

Also, i just replaced the heater core, and after replacing the heater core, the heater works wonderfully, but then i turn on teh air conditioner, to full blast all the way on the blue(cold) it blows out HOT air, if i leave it on for say 15 minutes the air just gets hotter!! Any ideas as to what causes this problem? also when i turn off everything, all the heater, ac, vents, and just everything, i still have warm air blowing out very lightly from the bottom vents, any ideas?

Also none of the interior lights inside of my car work, these also stopped operating after i took out the dash and replaced the heater core, the fuse continually blows, even after i replace it, it blows again? What could be causing this? Everything else works in the car, thank goodness, but those two problems, just take away from the car, and i would like to fix them if anyone has any idea's, especially the lights, well summer is coming, and atlanta is hot, so i think the air conditioning first!!

Antoher problem, when i hit the brakes hard, the front end shakes and grinds a little, i have been told its because i have warped my rotors, i think its getting worse! IS this something that needs to immediately be replaced? Thanks for all the help.

they say a new problem the occurs after a repair is made
probably isn't far away from whatever you were messing with last. one of the wires in the lighting circuit is shorted to ground it might be pinched by the dash somewhere. you should replace the motor mount as soon as possible it's not a huge or expensive job, just jack up the engine a little with a wood block under the oil pan and change it. the heater problem could be a broken/stuck blend door or vacuum line unhooked or in the wrong spot. by carefully going over your work you should have all the bugs worked out in no time. good luck

Sounds like you probably caused your own problems, There is a courtesy light socket right under the dash where you were working follow those wires and look for cuts or pinches. Look in the same area for vacuum lines that were probably pulled off during the core install.

Thanks for all your help, i really appreciate it, i figured as much that i caused my own problems, ooops, i am only 18, still learning though!! Oh well, better luck next time, but thanks again for the help, its quite appreciated, God Bless