When you look at the back of the drive, there should be at least three sets of connectors: the power connector, with its four large pins, the PATA connector with its 20x2 small pins, and the jumper pins, which are at least a 3x2 sections of small pins which look just like the PATA pins. There should be a small plastic plug, the jumper, pushed over the ends of two of these pins. The purpose of this is to make electrical contact between them, like a switch, and so if you take it off and look at it there will be metal contacts inside. When putting it back on, almost all drives that I have seen have the pins paired up and down; that is, when the jumper is on it should be perpendicular to the top of the drive. Lets see if I can illustrate with some ASCII art.
jumper pins with plug on set #3
power | PATA connection
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