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I need help identifying which wire is which inside my USB cable. So I stripped the outer insulator for the USB cable, and it revealed 4 wires: Red, White, Green, and Yellow.

I thought Red would be VCC, but then I checked the circuit board for the mouse I ripped it off of and the board labeled where the four wires were soldered on.

It showed four characters each associated with a wire color: V (White), G (Green), D (Yellow), C (Red). Very strange from what I have learned about USB so far, but strangest being that Red is not VCC! Why is there no standard for these wire colors?

Anyways, how can I confirm which is which (VCC, GND, D-, D+)? I have a multimeter, and confirmed that between White and Green, White and Red, and White and Yellow, there is 5V. I don't think that is much of a development, but what should I do?

I do have other USB cables lying around as well, but that's an easy way out and my absolute last resort. Thanks.

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Test connectivity between each exposed wire and the pins on the connectorized end of the cable? – The Photon Aug 22 '12 at 17:31
And then once you know which pin on the connector corresponds to which wire... reuk.co.uk/OtherImages/usb-connector.jpg – Nick Halden Aug 22 '12 at 17:34
@ThePhoton Sorry, what do you mean? It sounds like a statement and question mixed accidentally, and I'm unfamiliar with the term connectorized - sorry, I'm new to electronics. – capcom Aug 22 '12 at 17:39
@JGord Apologies if I was unclear, but the part I am having difficulty with is finding out which pin on the connector corresponds to which wire. Do you mean I should dissect the male end of the cable to see where each wire goes and work backwards? – capcom Aug 22 '12 at 17:41
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Photon means to test the wires against the pins on the connector, so that you can say "red = pin 1" etc. The pin assignments are unambiguous. – stevenvh Aug 22 '12 at 17:41
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2 Answers

up vote 2 down vote accepted

It's easy to just test the connectivity from the pins on the connector-end of the cable to the bare wires at the other end.

Even a hardware store multimeter is good enough for this test.

Disconnect the cable at both ends. Set your meter to the ohms function.

Touch one probe of the meter to one pin of the connector. Touch the other probe to one of the wires. If the wire is connected to the pin, you'll see (near) zero ohms. Depending on your meter you might also get a beep for continuity.

The pin assignments for the connector are readily available. Here's a picture from Wikipedia: enter image description here

If your connector is a mini or micro type, those pinouts are also available from the Wikipedia article on USB.

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Sorry, I thought I had an answer, but I don't (and the system won't let me simply delete it).

What the others are saying is that you should use your ohmmeter to verify which color wire at the mouse end is connected to which contact at the computer end, as shown here.

If your meter probe is too fat to reach the contacts in the connector, wrap a short piece of stiff wire (or a cut-off component lead) around it. There should be no need to take the connector apart.

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"I have yet to find one that does not follow the standard". Apparently it happens. Read the comments here. – stevenvh Aug 22 '12 at 18:24
His cable doesn't even have black, so it can't be following the convention you listed. – Ben Voigt Aug 22 '12 at 18:24
For reference, I discovered that Green --> GND, White --> VCC, Red --> D+, Yellow --> D-. Thanks for your answer though. – capcom Aug 22 '12 at 18:32
@Dave - we were leaving this for ThePhoton, he suggested this. Now it looks like you're stealing his answer, and that doesn't look nice. – stevenvh Aug 22 '12 at 18:42
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@stevenvh, no worries. I think he first posted a convention for the wire colors, then wasn't able to delete. Dave, if you want we can flag it for the moderators and they can delete it. – The Photon Aug 22 '12 at 19:02
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