1997 Mitsubishi Mirage

Electrical problem
1997 Mitsubishi Mirage 4 cyl Front Wheel Drive Automatic 150K+ miles

Nine months ago, I had to have my alternator replaced. Afterward, I took my car in for some routine maintenance and they told me that the bad alternator had caused the " main fuse" to go bad, and that it would have to be replaced, which they charged me 27.99 plus an hour labor for. The alternator went out again, I replaced it under warranty, and my car is still stalling, vibrating, and making noise, just as it was the last time. However, none of the auto parts stores I have been into know what exactly a main fuse is. Can someone tell me what other name it might be under? Or did my mechanic rip me off by saying they replaced a part that doesn't even exist?
Thanks in advance for any help.
April 29, 2010.

Check and test all the fusible links in the centralized junction block left side of engine compartment.

Apr 29, 2010.