Rear Speaker Wiring Polarity
 

I'm replacing the rear speakers in my 2000 Boxster S. Does anyone know the wire polarity (which is plus and which is -)? From past experience I suspect the wire with 0.25 Faston is positive and the one with the 0.125 Faston is negative.

should not matter as long as all of them are the same If the front and rear are out of phase, should not matter a lot as they are different distances from your ears and therefore the sound will reach your ears at a slightly different time anyway.

You could check the dash speakers and see how they are wired

I don't know the answer to your question. I do know that polarity is important. Speakers move air outwards when wired correctly. If the polarity is reversed the speakers is drawn inwards. This can eventually destroy a speaker. The moving parts of the speaker essentially bottom out on the frame work. The higher the volumes and lower the frequencies the greater chance of damage. For higher frequencies, you create a situation know as cancellation. The sound will tend to be hollow. You will most probably think that the balance or fade is off. Knob adjustments will not correct this condition.

Call the tech support at Crutchfield: Car Stereo, Speakers, Home Theater, Pro Audio, 4k TV They have been very helpful over the years.

Sorry Rex, but you are very wrong
I did pro audio for about 15 years and toured with some of the biggest acts in the world.

A conventional loudspeaker has several parts

Basket (frame)
Magnet
Voicecoil
cone

It is basically an electromagnet that the coil is energized and moves in and out of the magnet. The cone is attached to the voice coil and moves in and out with it. As it moved, it moves air at the frequency that is powering the voice coil. this movement of air is what makes the sound. Low frequencies are physically larger and require more air movement, hence larger speakers. Higher frequencies are smaller and require smaller diaphragms/speakers
The voice coil moves evenly in both directions. On the positive side of the waveform, the speaker moves out and the negative side inward. Connecting the "backwards" will merely make the speaker cone's movement be 1/2 cycle off from one wired the other way. IT DOES NOT CAUSE ANY DAMAGE!!!

It will NEVER destroy a speaker being out of phase with another speaker!! If the voice coil is bottoming out, it is broken or just a crappy design.

All being out of phase can do is lower the audio level you hear as there would be some cancellation, however that is only the case when all of the voice coils are aligned in the same plane. If they are not in the same plane, then to get perfect phasing, you would need to delay the signal to the ones that are further forward to get them timed correctly. This is true regardless of the frequency or volume level or power

Since this is a car and a small one for that matter, it is really impracticable and in reality we are at worst talking about a millisecond or so probably less.

If you are really concerned about getting the front and rear speakers in phase with each other, try it both ways and see if you can actually hear any difference. If you can leave the hooked up the way that sounds best to you.
In fact, having the front and rear out of phase with each other could actually sound better as the time it takes to reach your ear is different for the front and rear speakers.
This is because if both front and rear speakers are pushing at the same time they in effect are going to push into each other and cancel each other out. In reality they probably does not happen as you are not equal distances from each voice coil.
That is why some people want their systems time aligned, which in effect is phase aligning them. That however requires making very small changes to the delay in the signal for each speaker

At the end of the day, you probably can't hear the difference anyway in a car, especially with the top down

I'll say it again.
IN NO WAY WILL HOOKING THEM UP OUT OF PHASE CAUSE ANY DAMAGE!!!! it is physically impossible

As Jay G mentions, having it out of phase on the either the front or rear can be benificial. I have had all my SQ car installations (previous cars not my 986) out of phase on in the front.

Trying is both ways to see what sounds better for you is a good option.