I was wondering if anyone else is having the same problem. I've replaced the factory car radio and 3 of the 4 speakers have stopped working. I installed the new stereo about a year ago. I'm completely baffled by this. Thanks in advance...
You will need to get a multi-meter and do some troubleshooting.
Speakers tend to last a long time if they are treated well and are kept in a good environment for them, and are not used past their specifications.
So given all that...
1 - When you replaced the speakers were the new ones the same ohms and wattage as the old ones (mine were 40 watts)?
2 - Is the back window clear or piled with blankets and other stuff that could cause the speakers to over heat?
3 - Is pop/soda or other liquids constantly spilled on the insides of the front doors?
4 - Are you running the stereo through an after-marker amplifier whos output exceeds the wattage ratings of the speakers?
Anywho... Considering that all of the above is not an issue...
Get out the multi-meter and put it on the lowest OHMS range that it has and disconnect the cables from the speakers and test each speaker, you should get something close to what is marked on the speaker (usually 4 or 8 ohms).
If you have an 8 ohm speaker and are only getting like 1 or 2 ohms again check the multi-meter and make sure its set to the lowest ohms range that it has, considering that it is set correctly then your speaker's windings are shorted.
If you are getting an "Infinity" reading the speaker coil is blown, but in either case shorted or infinity the speaker will need to be replaced.
Considering that all of your speakers are testing ok then you are either left with a wiring problem to the speakers or your stereo has gone bad, check the connector on the back of the stereo there are four sets of wires that sort of match each other these are the wires that go to the speakers.
If those all test ok (ohms wise) then your stereo is bad, yes its only been a year but they just don't make things like they used to.