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I have a ribbon cable that is not labeled and does not have a notch to prevent it from being installed backwards. How can I identify which pin is #1 on the connector?

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5 Answers 5

up vote 11 down vote accepted

Pin 1 on a ribbon cable (the cable itself, not the terminators) is usually colored differently than the other pins - often red.

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This is correct. –  Troggy Jul 31 '09 at 19:37
    
It is, so long as you then know what pin #1 on the socket is... –  Alistair Knock Jul 31 '09 at 19:40
3  
I'm assuming you have an IDE (ribbon) cable so, typically on motherboards, they'll mark a '1' on the board to indicate pin #1. For IDE cables, newer motherboards have a open tab in the connector so that the cable you insert into the interface can only face the correct way. The interface on the cable will usually have filling tab to eliminate confusion. –  osij2is Jul 31 '09 at 19:46

You could use a multimeter to identify it, and the label/mark it for future use.

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Won't do you any good when the other 30 or so pins also have voltage on them. –  Alex S Jul 31 '09 at 19:54
    
From where? The intent is to test the cable directly, not while the cable is connected to anything. –  DHayes Aug 3 '09 at 12:14

See which edge of the cable (the cable, not the connector) is painted.

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Usually flat cable has one of it strand with a colored strips (usually red). So pin #1 will be on that side. if the pins are not lined up in the connector it will be the one the furthest to the side.

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Im not sure why sangretus response is doing so well. According to your post the ribbon is not marked. Additionally, the cable is just a wire so "wire #1" is arbitrary.

On the motherboard side osij2is is correct, they should have a #1 printed next to the terminal. On the other side your hardware user manual should help you determine where pin #1 is.

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That being the case (and I'm not equipped to say that it is), it then doesn't matter which way you connect the notchless/pinkless/labelless cable, so long as both ends are oriented toward pin #1 correctly, and therefore you are more correct. –  Alistair Knock Jul 31 '09 at 20:07

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