Car Stereos: No Sound, protection circuits, factory radio

Question
I recently in stalled a aftermarket Kenwood KDC-138 in a 2002 F350 Super Duty. The factory radio played fine but the face was damaged (company vehicle) so there was no way to operate the radio. After installing the Kenwood, I had no sound. I used a harness adapter to go from the radio to factory harness. Checked all connections, good. Antenna, good. Checked factory harness connections, good. I checked these over and over. The unit powers on. All controls work fine. But no sound from, AM, FM, CD, or aux. When powering on the right rear speaker makes a quick pop sound then nothing. No other speakers make the sound either. One thing I have not tried is wiring one speaker at a time. Though if there was a short, why did it not show up with factory radio. Any idea that could help out?

Answer
Hi Chase,

After-market head units often have pretty sensitive built-in protection circuits, so it's not unusual for a speaker wiring issue to cause an after-market deck to shut down when a factory radio will still play.  It definitely sounds like a speaker or speaker wiring problem, and the right rear speaker is the prime suspect.  Your idea of connecting one speaker at a time is a good one; another option would be to use a multimeter to test each of the speaker wires at the head unit location to see if one shows continuity with chassis ground.  

This problem can be caused by a defective speaker or a shorted speaker wire.  If you narrow it down to one particular speaker, you can try disconnecting the speaker itself and see if that solves the problem.  If the head unit will play with the speaker disconnected, then you'll need to replace it; if it still won't play, you may need to run a new pair of wires between the head unit and speaker, to bypass any short in the factory wire run.

Don't forget that a pinched speaker wire or bare connection at the back of the head unit can also cause this problem.

Hope this helps!

Brian