How can check if my alternator is blown?

I just recently hooked up a amp and sub to my car. It's hooked directly to the main battery and now my car won't start up. My lights works fine and my radio comes on and off. Do you think taking off the amp wire will solve the problem? I went to the autoshop and they say I need to replace my battery. But other people suggest that it is my alternator. How can I be sure? Thanks for the help.

EDIT: To give you guys more info, when I jump start the car it runs fine, but when i turn off the engine i started it up once, but most of the time I can't. I measured the DC volts with a battery meter and it reads 10.61.


Modified by layzie21 at 6:14 PM 1/13/2005

 

do the lights dim when you try and start it

 

Yes its dim, and my windshield wiper moves sluggishly.

 

ya you need a battery and possibly an alternator have what is the voltage at the battery terminals with the engine running

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b16h22a &raquo;</TD></TR><TR><TD CLASS="quote">ya you need a battery and possibly an alternator have what is the voltage at the battery terminals with the engine running</TD></TR></TABLE>

How can i be sure if my alternator is bad? Is there a way i can check? I have to jumpstart my car to check the volts tomorrow so i will definately get back to you.

 

well i know autozone tests them for free but when you get the new battery with the engine running is the voltage is from 13.5 to 14.5 then you should be able to get by with just a battery but if it reads in the 12 volt range with the engine running then you need a new alt also