Car Stereos: 1998 jeep grand cherokee aftermarket stereo help, jeep grand cherokee, using a digital multimeter

Question
hey brian, i have a 1998 jeep grand cherokee, i replaced the stock deck with a kenwood cd deck. I recently installed a alpine 200w amp with a 400w sony explode sub. the problem i'm having is that when my stereo is on without the amp\sub it works fine, but when the amp is hooked up the deck will stay on only when it's in standby mode as soon as there is sound my deck and amp turn off. i have to unplug the harness from the deck itself and plug it back in for it to work. but as soon as the sub kicks in the decks shuts down i've checked fuses, grounds, power. i used an amp kit and everything i know is wired in right.......please help before i lose more hair than i don't already have

Answer
Hi Todd,

Unfortunately, this isn't a problem that I could solve very quickly without doing some hands-on testing.

From your description, it sounds like the head unit is losing power completely, and the amp is just shutting off because the head unit is shutting off.  In general, if I'm checking any sort of power problem, I'd start by using a digital multimeter to test the power and ground wires at the back of the head unit.  Set the meter for DC volts, connect the black probe to the black ground wire, and the red probe to the yellow power wire.  Watch the voltage as you start playing the sub.  If it's dropping below about 11 volts, then there's a power problem that needs to be addressed.

Because the problem isn't occurring until the amplifier is in use, it seems likely that the amp is causing some sort of strain on your vehicle's electrical system that's affecting the head unit.  I'd check the battery terminal connections--make sure they're clean and tight.  There should be a cable that runs from the negative battery terminal to the vehicle chassis; make sure this wire is securely connected at each end.  Also, double-check the new head unit's ground connection: in your Grand Cherokee, the factory ground wire is usually either a braided metal strap, or a black/green wire, which was originally attached directly to the stock head unit's chassis.  Make sure the new deck's ground wire is connected to the original ground wire, or directly to chassis metal.

Hope this helps!

Brian