Determining - and + on 12v?

[blueonblack]

I'm wiring a plasma ball into my case, and the one I got is different from any of the ones I've been able to find on the Internet. The plug for the wall has a 12-volt converter already on it, so it has 12-volt DC going into it through two wires and a round connector. I should be able to cut the converter off and wire on a Molex connector and hook it straight to the PSU, correct? 12 volts DC either way.

Problem is, I have read that I have to determine which wire is positive and which is negative, and there is absolutely no indication on the wires, they are very small (18 gauge at most) and identical. Is there a way to determine positive and negative wires? Anything I need to know before wiring this up? I already let the magic smoke out of one plasma ball and have no idea how, hate to have to buy another one. Any advice would be great, thanks!
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Suzuki gt series history (http://www.suzuki-tech.com/wiki/Suzuki_GT_series)

[SgtM]

Does one of the wires have a stripe on it? If so, that's usually negative.

[blueonblack]

Ooops. Ok, they are not identical, they are black with VERY faint gray printing on them. Under the right light and a magnifying glass, one has a series of dashed lines down its length and the other has words on it relating to wire size, voltage and type of wire. Would the dashed-line wire be my negative?
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Lamborghini murci?lago history (http://www.lamborghini-tech.com/wiki/Lamborghini_Murci?lago)

[SgtM]

You can bet that 99% of the time, that is going to be the negative.

[blueonblack]

You can bet that 99% of the time, that is going to be the negative.

This must be the 1%. :) I hooked a meter to it with negative to the dashed wire and positive to the other and got a negative voltage reading. Reversed, it reads positive 12 volts as it should. This tells me the dashed wire is the positive, would anyone agree? (Before I fry another plasma ball?)
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PETER COLLINS (RACING DRIVER) (http://www.ferrari-wiki.com/wiki/Peter_Collins_(racing_driver))

[SgtM]

Strange.. if that's what the meter says, I would go with that.

[Drum Thumper]

One question before another accidental sacrifice--do you have your leads hooked up to your multimeter correctly?

I realize it's a no-brainer, but these things do happen.

[blueonblack]

Yes I do, that was in fact the very first thing I made certain of. :)

(and yes, these things DO happen, all too frequently)
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VAPORIZER SHOP (http://vaporshop.com)

[J-Roc]

check the amps and volts on the wall adapter. You wouldnt want to fry your PSU by drawing too much power.