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Discussion Starter · #1 ·
Can you use a multimeter to determine polarity on wire that is unlabeled (potentially while music on)? Wires were connected to factory rears to run to amp high level in. Those bare wires will power a test 5x7, just unsure of polarity when wiring my high level adapter.
 

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If it's a woofer (doesn't really work with tweeters) you can touch the wires to a battery and see which way the cone moves. Don't leave it connected, you just need to quickly touch the wires to the battery.
 

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Discussion Starter · #3 ·
Thanks for the input. I've seen that suggestion, but I am looking for wire polarity, not the speaker polarity.

This is what I've got:

wire loom along floorboard was tapped for left rear and right rear speakers to be used as high level inputs

the wires that I added are run under the carpet to the amp location

those wires are unlabeled

the rear door speakers still work, and when I connect a test speaker direct those those wires I've run to the amp, it plays just as the door speakers do (polarity is not an issue here)

however, I need to connect the left and right rear +/- to the appropriate polarity on the high level harness provided with amp

can I use a multimeter to check those bare wires, prior to splicing to the high level input plug, potentially while music is playing (or otherwise)?
 

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Maybe using a diode would help whole an amp is running?

But usually one just a uses a DMM lead near at amp, and then test each side at the speaker...
On the correct side with the wire is 0 ohms And the wrong side is 2, 4 or 8 ohms.
 
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Discussion Starter · #6 ·
These wires are not labeled at all, I soldered to L/R rears on the loom and fed wires under carpet. Idiot/lazy move using these wires, they were just what I had.

Imagine these bare leads coming out of carpet, they are live rear speaker wires run in parallel with rears for the purpose of connecting to high level amp input. Can I not read AC voltage on the bare end while they are hot? I am just afraid to fry something checking with multimeter...
 

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Discussion Starter · #7 ·
This is best I've found...

Q1. Can a conventional voltmeter be used to check the unit's speaker output?
A1. Yes, set voltmeter to its AC (alternating current) selection and use that 15-volt scale you mention your meter having. Run the head unit's volume level fairly high and watch for variable meter pointer movement (or indication if the meter is a digital type) corresponding with the audio program material. The output from a head unit's speaker output is audio, that's AC voltage, so it matters not reversal of the meter's connection leads to the two wires from each of the head unit's audio channels. When wiring connection errors are a possibility it's far best to disconnect all the car's speaker wiring from the head unit so meter indications don't get confused with audio outputs for other speaker channels.

credit Jeff Anderson:
https://forum.miata.net/vb/archive/index.php/t-207624.html
 

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This is best I've found...

Q1. Can a conventional voltmeter be used to check the unit's speaker output?
A1. Yes, set voltmeter to its AC (alternating current) selection and use that 15-volt scale you mention your meter having. Run the head unit's volume level fairly high and watch for variable meter pointer movement (or indication if the meter is a digital type) corresponding with the audio program material. The output from a head unit's speaker output is audio, that's AC voltage, so it matters not reversal of the meter's connection leads to the two wires from each of the head unit's audio channels. When wiring connection errors are a possibility it's far best to disconnect all the car's speaker wiring from the head unit so meter indications don't get confused with audio outputs for other speaker channels.

credit Jeff Anderson:
https://forum.miata.net/vb/archive/index.php/t-207624.html
This will not tell you anything about the wiring polarity. Did I read correctly that these wires will be the high level inputs for an amp?
 

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Discussion Starter · #9 ·
This will not tell you anything about the wiring polarity. Did I read correctly that these wires will be the high level inputs for an amp?
Yes you did. Should I just wire the high level input adapter to the bare leads and try it? Is polarity important in wiring the adapter? Or, do I just need to match the polarity orientation between channels?

Image from amp manual:

259096
 

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If you are feeding those wires into the high level inputs of an amp, you don’t really need to worry about polarity. If one speaker ends up wired in reverse polarity then you can just swap the speaker wires and put it back into the same polarity as the other speaker.

I'm not not sure what that warning is getting at. If you have speakers wired in opposite polarity, they will be 180 degrees out of phase. This does not result in "complete loss of signal" but it will reduce the bass, because there will be destructive interference with the sound waves. Wire it however you want, then once you've connect the speakers flip the wires on one of the speakers. Do that back and forth a couple of times, and whichever configuration gives the best bass will be the configuration that is wired correctly in phase.
 

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Discussion Starter · #11 ·
If you are feeding those wires into the high level inputs of an amp, you don’t really need to worry about polarity. If one speaker ends up wired in reverse polarity then you can just swap the speaker wires and put it back into the same polarity as the other speaker.

I'm not not sure what that warning is getting at. If you have speakers wired in opposite polarity, they will be 180 degrees out of phase. This does not result in "complete loss of signal" but it will reduce the bass, because there will be destructive interference with the sound waves. Wire it however you want, then once you've connect the speakers flip the wires on one of the speakers. Do that back and forth a couple of times, and whichever configuration gives the best bass will be the configuration that is wired correctly in phase.
Kind of what I was hoping you would say. I'll report back.
 

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Can you not see the color of the wires you connected to ? Are you sure the rear output of the stock headunit is full range ? If it is for a sub amp, may not have a full bass signal. If it is for a full range amp, you might get a bandpassed signal.
 

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Makin' music now! Hooked it up properly the first time. Took it apart and tried an alternate config, got worse.

Thanks to all that provided input.
Just to clarify, either way will make music, and the difference won't likely be obvious expect for in the lower frequencies. As long as you are certain with the results of your A B test, you're good, but be aware that the differences will really only be obvious in the low frequencies, so make sure you've tested thoroughly before deciding on the correct polarity.
 

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Discussion Starter · #15 ·
Can you not see the color of the wires you connected to ? Are you sure the rear output of the stock headunit is full range ? If it is for a sub amp, may not have a full bass signal. If it is for a full range amp, you might get a bandpassed signal.
When I soldered yes. Wrapped the + in tape. When I pulled under carpet I lost tape, didn't realize until I buttoned everything up. Just too lazy/stubborn to pull those wires back through and check it. Also, was genuinely curious if there was a method to verify with multimeter.
 

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You could use meter to check for continuity, and if you have the car harness wiring chart determine which is + or -
 

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You could use meter to check for continuity, and if you have the car harness wiring chart determine which is + or -
The problem is that he doesn't have access to the OEM wires. He soldered his own onto the OEM wires, then buried them under the carpet, leaving only the unmarked add on wires exposed. Continuity doesn't help determine the polarity.
 

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Just a way. Not the easiest but if he has wiring diagram it would be correct. Tbh he could check continuity from the radio harness back if there isn't a factory amp/processor involved. Just not the easiest way
 

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But, what good will the wiring diagram do if he doesn't know which wire is which? He'd still have 2 un-labeled wires to work with. Am I missing something?
It's not like he can't check for continuity. Like I said it's just not as easy as labeled wires. Another alternative is an o-scope but that's way harder than wiring diagram and continuity
 
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