subs shutting off

my partna is having troubles in paradise...he has a 2008 chevy impala with the factory radio installed runnin two 12" kicker L7 4ohm load. the problem is when he turns the system up the subs shut down, the other speakers are still playing. we just finished looking at the wiring to the subs, but i didnt see n e thing out of the ordinary. plus his lights are diming really bad. He has confused me with this one so im looking for some help for him. Set-up: Factory h/u rockford interface for subs kicker 1500.1 mono amp (turned 1/4 up) (2) 12" kicker L7 optima yellow top bat 20 farad rockford cap

One of several things, but most likely one or both of these: 1) amp gain is too high, 2) your alternator cannot keep up with the load and system voltage is dropping too low.  Read the "How to set your gains" post in the Hot Topics forum, and measure your voltage as I bet you need to upgrade the Big 3 and probably invest in a new high output alternator as well.Support the12volt.com

Did you use a meter to make sure the woofers are wired at 4 ohms?

the speakers are rated @750 rms per sub and the amp is a mono 1500.1 when i said 1/4 way up meaning that the amp is bearly turned up, but i will have him check the the alt output... we use the wiring diagram per this site for the wiring of the subs also...

how do you check the ohms that ur running using a voltage meter

Add a current meter R = v/i Most use multimeters and set the resistance (Ohms) range into UNPOWERED impedences (load, speakers etc).

With the amp turned off, you can have the speakers connected to the amp.  Set the meter to the Ohms selection.  Touch one meter lead to one speaker terminal.  Touch the other lead to the other speaker terminal.  The woofers need to be as still as you can possibly have them to get an accurate reading.  No other speakers in the car playing.  No woofers playing in the next vehicle.  The amp must be off, not volume turned down, the amp must be powered off.

I'm gonna vote that they're dual 4 ohm subs wired to 1 ohm.A DMM is a beautiful thing.

MECP Advanced Installer Certified.

i think its because your factory radio is not enough power for your amp.and the one speaker output is sucking all the juice from that one channel.,

Wow