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I have a device which has a dc barrel jack with inside + and outside -. If I plug in a barrel connector which has 2 wires to connect to a DC voltage source (battery) how do I know which wire to connect to the positive terminal and which wire to the negative terminal?

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    \$\begingroup\$ use a continuity tester \$\endgroup\$ – jsotola Dec 21 '17 at 3:12
  • \$\begingroup\$ Some Chinese Stuff has DC barrel connector with Pos on the outside and Neg on the inside so be catreful . \$\endgroup\$ – Autistic Dec 21 '17 at 4:33
  • \$\begingroup\$ Almost all stuff has +ve centre, -ve outside EXCEPT guitar effects pedals (as I found out to my surprise a few months ago) \$\endgroup\$ – Neil_UK Dec 21 '17 at 6:09
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Not all cables have printed polarity indicators, so your best bet is to use a multimeter in continuity testing mode as mentioned by @jsotola.

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