Power wires will run from the power supply to the motherboard, diskette drive, and some expansion cards in the expansion bus, such as the diskette drive controller. Not all devices draw power from the power supply. Some, such as the video controller, will take all the power they need from the expansion slot socket. If your computer uses a small fan to keep the microprocessor from overheating, a small power lead will run from the motherboard to the fan. Data transfer wires connect the disk drives to the motherboard.
Wires connect some devices inside the computer to indicator lights on the exterior of the computer.
For example, a wire leading from the drive controller indicates when the hard drive is downloading data to the microprocessor. Every time you disconnect a wire or a cable, make a note on your sketch. With the exception of the larger connectors for the ribbon cables, there should be a small mark on the motherboard. This information will help you when you are reconnecting the wires and cables to the proper plugs after you install the motherboard. Now, remove any expansion cards from the old motherboard's expansion bus.