Car Stereos: Power, but no sound from aftermarket stereo., external amplifier, stock speakers

Question
I connected an aftermarket stereo to replace the stock stereo in my car, but after connecting everything, the deck powered on, but no sound came from the speakers. I used a wire harness and even went through all of the wires again to make sure everything was connected right. I reconnected the stock stereo and it worked fine. Do you have any ideas of what the problem could be?

Answer
Hi Chris,

There are three possibilities.

First, your vehicle may be equipped with a factory amplifier.  In this case, the amplifier needs to be activated when the after-market deck is turned on.  Different vehicles have different methods for integrating an after-market deck with a factory amplifier.  If you can follow up with the year and make/model of the vehicle, then I might be able to give you more detail about this.

Second, there may be a problem with a speaker or speaker wiring.  If there's a short-circuit condition on any speaker wire, a typical after-market head unit will go into "protect" mode, shutting off the sound to all the speakers.  If you used an adapter harness, and the stock speakers are still in place, then a shorted speaker wire is unlikely.  However, if one of the speaker wires is getting pinched behind the deck when it's mounted in place, that could certainly cause your problem.  Also, if your factory speakers were replaced with after-market upgrades, it's possible that there's a shorted wire at one of the speaker locations.

Third, it's possible that the new stereo is defective.  

Here's how I'd troubleshoot the problem:  First, investigate the possibility of a factory amplifier.  If you're certain that there's no external amplifier in the vehicle, and that the speakers are connected directly to the head unit's speaker outputs, you can use a multimeter's continuity function to see if one of the speaker wires is showing continuity with chassis metal.  If you don't have a multimeter, try disconnecting all but one of the speakers.  If you get sound with a single speaker connected, re-connect the others one at a time until you identify the speaker that's causing the head unit to cut out.  If you don't get sound with a single speaker, disconnect that one and try a different one.  If you still get no sound, and you're certain there's no factory amplifier in the vehicle, then it's likely that you have a defective head unit.

Hope this helps!

Brian