Audio Systems: subwoofer problem with cars computer, transient spikes, mercury sable

Question
i have a 1993 mercury sable and about a year ago i had a subwoofer system
installed at the local circuit city. everything worked great for about three
months when it decided to stall while i was driving. we brought it to our
mechanic for the repair and 600 bucks later, he said that something [most
likely my subwoofers] caused a surge that fried the cars' computer. i thought
nothing of this and blamed it on the cars age and computer, but two months
later the same thin happened and i decided that it really wasnt worth the
money to repair the car again.

my real question would be, do you have any knowledge of similar problems
like this happening and was my mechanic correct? also my battery is
practically brand new and would i be able to fix this my self?

thanks again!

Answer
While I have not heard of this exact problem, it sort of makes sense.  With the Sub on, you are drawing a significant amount of power, especially if you run it loud.  I would guess that you were on the edge of what the alternator could provide.  At that point the voltage regulator is also running at capacity.  It is easy to allow transient spikes to pass through the regulator or the voltage drops a bit and the computer ends up drawing too much current.
Golden rule:  always check the alternator capacity before installation of large amp systems.
Dan