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[ The PC Guide | Systems and Components Reference Guide | Motherboard and System Devices | The Motherboard | Motherboard Integrated Components ]

Pin Connectors

The motherboard provides several connectors that are attached to the case LEDs, indicators, and switches. These (as usual) vary by motherboard, but the ones described here are typical. The physical layout of these connectors can vary a lot as well; some motherboards physically separate these connectors on the board while others group many together into a large "multifunction connector". Functionally there is no difference but it is easier to make an "off by one" connection mistake on a multifunction connector.

Note: The LEDs on the case are a form of diode, and this means in part that they will only conduct electricity in one direction. This means that if you connect them backwards, they will not work. However, they usually have a protection circuit in them so that if you connect them backwards they will not be damaged, and you can just switch them. Your manual or (less commonly) the board itself may provide an indication of which pin is positive and which is negative on the motherboard.

These are the pin connectors you will typically find on a modern motherboard:

  • Power LED and Keylock Switch: These are two different functions, each requiring two pins, but for historical reasons, they are often combined into a single 5-pin connector. Older cases had the keylock and power LED wires going to a single 5-pin plastic connector. On newer cases they are often separated (in fact many newer cases have no keylock switch) but the 5-pin motherboard connector remains for compatibility. Here is its usual configuration. Note the unused pin between the two power LED pins:

Pin #



Power LED Output (positive)


No Connection (NC)


Power LED Ground (negative)


Keylock Signal (positive)


Keylock Ground (negative)

  • Reset Switch: This 2-pin switch has no polarity so you can connect it either way.
  • Turbo Switch: Another relic of the past, many motherboards still include this connector, even though it ceased having any real meaningful purpose after the early part of the 486 generation of motherboards. In most cases it is best just to leave it unconnected.

Warning: Some motherboards (especially older ones) default to "turbo off" if not connected to a switch. If you are installing a motherboard of this type, you must jumper (short) the turbo switch pins if you are not going to connect the turbo switch. See this section of the Optimization Guide for more details.

  • Power Switch: On ATX systems there will be a connector for attaching two leads from the case power on/off button. On ATX PCs the power switch sends a signal to the motherboard to turn on the PC; it doesn't attach directly to the power supply as it does on older AT style systems.
  • Turbo LED: This is the counterpart to the turbo switch of course. I sometimes connect the LED to this connector if the case has one even if there is no turbo switch, as then the light will come on (which avoids confusion as to "why the turbo light is off").
  • IDE/ATA Hard Disk Activity LED: This connector signals the LED when the motherboard detects activity on any of the system's IDE hard disks. Some motherboards have four pins for this connector. On many of these the four pins represent two different pairs, both of which work: pins 1 and 2 are one pair and 3 and 4 are another, and either pair can be used. On other motherboards, only two of the pins can be used; you need to check your motherboard manual.
  • Speaker: This is a 4-pin connector for the case speaker, but only the two outer wires are used. There is no polarity here either, you can connect the speaker either way.
  • CPU Fan: Some motherboards have a 2-pin connector for powering the processor's fan, if the fan has the right type of power connector. Many fans just connect to the regular power connectors from the power supply.
  • Suspend Mode Switch: Some systems have a two-pin connector for a toggle switch to put the system into suspend mode. The turbo switch button on the case can be used for this function on newer systems.
  • Suspend Mode LED: Some systems have a connection for an LED that is lit when the system enters suspend mode, either by using the suspend mode switch or through automatic power management.

Next: System Chipset and Controllers

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