Next you should unplug all the connectors coming from the power supply. Some motherboards use one connector for power and others have a second smaller plug as well. After unplugging all the connectors, carefully turn on your pc being careful not to touch anything inside even though all the inside connectors are now disconnected.

Now locate the red wire on the connector that attaches to the motherboard. Set your meter to VDC, and put the red lead into the red wire connector and the black lead into the black wire connector. The black is a ground and the red wire should give you about 5 volts DC. This is one of the power sources.

The other main power wire is the yellow. Following the above instructions again, this time put your red lead into the yellow wire connector and the black into the black connector. Now you should be getting about 12 volts DC.

Tip: the case of the power supply must be grounded to the tower case in order to check for power at these wires. If you are in doubt of your readings, take your power supply into a service department and have it checked professionally. Power supplies are not cheap, and can be tricky to troubleshoot sometimes.

Here are the rest of the wires. Note that some supplies have many more wires and you should refer to the manual or wire diagram for your particular model:

Red = +5volts                                                                                                   

White = -5volts                                                                                                     

Yellow=+12volts                                                                                                    

Blue =  -12 volts                                                                                                  

Black =  Ground

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