Audio Systems: Subwoofer Trouble, how to use a voltmeter, volt ohmmeter

Question
I have a P3002 amplifier Rockwood Fosgate amp and subs.  My subs are controlled by a little box underneath the steering wheel that controls how much bass is put out.  There is a little light that is on when the subs are on.  Well,when my music is played on my Alpine faceplate the light will turn off and on every couple of minutes.  The subs kick on and then they kick off.  My system is been in my car for almost 3 years.

My friend suggested that in the trunk of my car which my subs sit there is a blue cord that has a prong that connects to this lugnut.  He said loosen it and then wiggle the cord to see if it comes on.  It worked but only for like a minute.  What is wrong with my subs and what do I need to do?

Answer
Sounds like a bad connection or loose wire somewhere.  Wiggling the wires will help you find it.

Do you know how to use a voltmeter? If so, or if you are willing to study the booklet that comes with it, go to Walmart or Home Depot and purchase their little volt-ohmmeter that is under $10. It is ideal for auto use.  Then, check the voltage levels on the amplifier.  The sub amp should have two 12v lines; one coming from a fused battery connection. The other from the box with the light.  Check the 12v on that line; it is the remote turn on for the battery.  Then, find out where the 12v turn on line is losing its 12v. You can do this by tracing the wire back until you get 12v.  The problem is wherever the 12v is lost.  Whether it be a connector, broken wire inside a lug, etc.

Happy hunting. Let me know if you need more ideas.
C