HELP-1st the cd player NOW the alarm system

We have a 96 pathfinder with 211,000 miles. It runs great since we faithfully do oil changes and maintenance. It started having some electrical ??? problems. The cd player would be trying to reject a cd even when there was no key in the ignition, plus we never used the cd player. This is ran my battery down. So we took the fuse out for the radio/clock/cd.
Now the alarm system goes off by itself. I have pulled into a parking spot and the pathfinder is still running but the alarm goes off. The only way I can shut it off is to get out and lock the doors and put the key in the door lock. It has happened about 5 times now. The garage that does our mechanical work, says they would not be able to fix it because they did not do electrical work. Does anybody have and idea as to what we need to do? Thanks

Update...
Had the factory installed security system unhooked... now everything
else works....