I spent a bunch of time checking the polarity of each of the speakers in my car using the android app I posted here. These results are after installing the diy wiring harness I received in mid to late november. my car (feb 2020 build) has the factory rear shelf speakers and wiring installed. your results will probably vary.
1. The front driver's door woofer is wired backwards
2. The right rear shelf speaker is wired backwards
3. All other speakers appear to be wired correctly.
Here are some tips I discovered that made testing more accurate:
1. You need to adjust the threshold level and volume very carefully to guarantee that you are only picking up the signal from the speaker you are checking. you want the signal meter to just show a little yellow past the threshold slider. I held the phone just in front of with the mic facing the speaker I was checking.
2. Use the balance control to only check one section at a time (i.e. left front, right front, etc.).
3. I used towels to further muffle the other speakers in the front while testing the tweeters. These were the most difficult to test accurately.
4. The app has the ability to flip the polarity of the test signal. I used this to double check my results. You should see the opposite result when the pulse is flipped.
5. I used a 80 hz pulse for the front door woofers, 500 hz for all the rears, and 1.2 khz for the front dash and door tweeters.
I'd really like to see the results of a car that hasn't had the wiring harness installed yet. If I get bored later this week I might undo mine to measure it myself. We'll see.
As for fixing it, I will probably modify the harness if possible especially if the results from the stock wiring show all the speakers are wired correctly (i.e. all positive). I'm fairly sure i can extract the pins and flip it in the connector but this needs more studying.
Free app I used:
https://play.google.com/store/apps/details?id=com.dwa_ict.polaritychecker