[NilsOlav]

After carefully listening to my new speakers, I noticed that the left speaker appeared to be slightly louder---I would notice singer's vocals specifically sounding as if they originated more from that speaker than the right speaker. However, after switching the left/right wiring in the back of the amp, I then noticed that the broader/louder sound came from the right speaker. Is this a problem with my wires, the amp, or something else? How should I try to fix this? It's not my ears and its not the speakers, I don't think.
 
Also, there could be a slight chance that the songs I used to test this did have a louder vocal part in the left speaker....so could someone recommend a good song with vocals that play evenly from each side?

 

[JustinBieber]

You could just play a flat tone with a frequency gen instead of trying to find the perfect song: http://onlinetonegenerator.com/

 

[SteveHiFi]

Use an old song, in mono.
 
It might be (this is my guess) that one  of the wires has a partial break - this would reduce the conductivity and raise the resistance within it, leading to the quieter sound. If you have a multimeter it may be worth measuring the resistance in the wires you have there.