Yes, I'm not a stereo expert. Car has a Sony Explod deck and Explod speakers. Wiring harness has 2 wires for each speaker. One plain, one with black stripe. Which one is positve/negative?

Also, speaker has pins, one large with red wire going into the speaker, one small pin with black wire and a weird blue curcuit thingy inline? What's positve/negative on the speaker?

Thanks, all was already in car when I bought it but it was wired hillbilly style, lots of splices, crappy wiring etc. Replaceing wire, less spices, better connections etc. Can't afford new stereo/speakers right now so I'm trying to resurect the old stuff.

Oh, also found a two channel Alpine amp tucked up under the dash with a whopping 18 watts per channel, thing looks pretty old and it's tiny. Think it was a dealer install?

There is no pos/neg with modern stereos. Stereos use a balanced approach where one wire goes positive and one goes negative to effectively double the amplitude of the music wave.

Either wire will work on either speaker terminal. Just don't ground either wire; they need to float with respect to ground.

Really? So why different color wiring, why different size pins on the speaker?

as long as you are consistant you will be fine. If you use the striped wire to the small pin just do the same on the other speaker.

As Lennie said, as long as you are consistent which wire goes on which speaker terminal.

The only difference if you swap plane and striped between speakers, the difference is that the speakers will be out-of-phase. That is, if the speakers played the same note, one speaker would be moving outward while the other is moving inward.

I'm not sure one would be able to perceive that the phasing is incorrect.

That's what I saws taught too. Do them the same so te speakers are in phase.

be consistent so the speakers will not be out of phase (whihc unless your ear is good you probably would not notice. All the stereo's I have wired used the white striped wire as your positve which in turn connects to red, negative would be your plain wire no stripe to black terminal. That 18 watt alpine may sound better than a new bonanza wattage blaupuinkt w/ leds and zoom whams..

The answer to your question will best be found in the manual for the devices. The wires do make a difference for several reasons. If they are reversed the speaker performs differently. I speak from 15 yrs. experience in the audio field. Check the manual for both the deck and speakers to determine which on is + and -. The "weird blue curcuit thingy inline" is most likely a capacitor of some value like 150uf for example. That is used to lower/block frequencies the speaker could fail when trying to reproduce. It does not help in determining + or - because it can be used on either.
I reference to Spokes comment. Yeah you can reverse the wires but this will affect the starting direction of the sound wave reproduced. Plainly speaking when the bass hits, hooking it up one wave the speaker will extend outward. When the wires are reversed the speaker cone will travel inward on the same hits.
And to all the other comments about out of phase...that is correct and he will hear the difference. you don't need to be a pro to notice notes that are canceling out.
Hope that helps

As an IASCA judge (International Auto Sound Challenge Assoc.) I can tell you it does matter which is positive and negative. Unless you are an audiophile, you may not hear the difference. It mostly comes into play for bass notes. I agree, if you keep consistant you will be OK but for the audiophile not so much. Your speakers also have a positive and negaive. If they are not marked, the smaller terminal is negative. If both terminals are the same, try this. Use a AA battery. connect the battery to the speaker terminals. when you see the speaker cone move out towards you and away from the housing, look at the battery terminals. Positive and negative will match the battery. If the cone moves away, flip the battery over.
Now in some cases it will sound better if the speakers are connected backwards. This is due to wave propgation between speakers. This can be good and bad. If the speakers face eachother, like in the doors. At certain frequencies you will have boith positive and negative wave propagation. Positive is when the two sound waves meet in the middle at the peak of the sine wave. This action causes that frequency to sound louder. Negative is just the opposite. When the sound waves hit eachother at the bottom of the sine wave. Depending on how far apart your speakers are from eachother, the frequency at which this takes place will be different. To try to avoid this, most speakers should be installed slightly off axis from eachother. Although due to refraction, this phenomena can still occur. It is at this point when you would want to try to reverse phasing and try to correct the sound. This can be done front to rear or side to side.
In my 914 I run door speakers and a woofer. I have to run the woofer out of phase with the door speakers because of negative propagation canceling the bass notes.

http://www.proavmagazine.com/acoustics/which-pin-is-hot.aspx

I might also add the caps are polarized on a lot of two and three way speakers, so you can loose highs and mids if wired wrong. This doesn't matter as much if you run separates.

I think you guys are making this way too complicated - call it good at keeping the polarity consistent. This is a 914, not a recording studio.

Ok, but really, how hard is it to get + to + and -to-. All modern stereos use the same color coding, and speakers are always labeled in some way. Might as well be the correct consistency.

RED +
Black with weird blue circuit thingy (capacitor) -