The numbering for power supply cables, differs from one pre-built computer manufacturer, to the next.
GENERALLY, a P3 power cable is a 4-pin Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
(Also misnomered as a 'Molex' power cable.
Molex came out with the design for the power cable CONNECTOR.
The name stuck. Kinda' like calling an adjustable open-end wrench, a 'Crescent wrench' )
A P4 power cable is usually a 4-pin ATX +12 Volt power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
This power cable was brought out to provide more power for the motherboard, and specifically the Processor. (CPU)
Does NOT connect to an optical drive. (CD/DVD drive)
DOES need to be connected to motherboard though, because it is POWER for the Processor!
Let's dispense with the antiquated numbering of the power cables, and show you the real information you need;
There are two types of Optical Drives out there, currently being used;
1) IDE. Also known as PATA.
An IDE optical drive will use a 4-pin Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
Note the rounded corners on top.
When plugging in one of these power cables, just always remember the rounded corners go on TOP.
The data cable used is a flat IDE ribbon cable. These are general examples,
I would like you to look at the connector end, and specifically the Locating Lug on one side of the connector,http://en.wikipedia.org/wiki/File:PATA-cable.jpg
This style of Locating Lug consists of two small 'bars'.
There are types where it is filled in. Just one solid lug.
The Locating Lug lines up with a Cutout, on the optical drive.
(Or IDE/PATA harddrive)
IF, there is no Locating Lug on your IDE/PATA flat ribbon cable, post back in a Comment.
I will show you the proper way to connect it, using the Red stripe on the side of the cable.http://en.wikipedia.org/wiki/Parallel_ATA
If you have a SATA optical drive, it uses a SATA power cable.
This is a general example,http://www.playtool.com/pages/psuconnectors/connectors.html#sata
Between the SATA data cable connector, and the SATA power cable connector; the SATA power cable connector is the larger of the two.
SATA data cable connector has 7 contact pins.
SATA power cable connector has 15-pin.
This is an example of a SATA data cable, and it's respective connector,http://en.wikipedia.org/wiki/File:SATA_ports.jpg
Note the L-shaped opening. The SATA power cable also has this L-shaped opening.
Observe the SATA data cable connector examples, on the motherboard.
Note the L shape.
(Note: The SATA data cable connectors on YOUR motherboard, may differ in style.
The ones shown (Red) are an Open design.
There are styles that are Enclosed. Have an oval around the
To install the cable connector, line the L-shaped opening, with the L shape on the optical drive connector.
Tip: Turn this L over to the left, then turn upside down.
The small 'foot' of the L, always points DOWN, when installing connector.
The SATA data cable connector, that plugs into the optical drive, should be a 90 degree bent elbow.
The connector end that plugs into the motherboard, should be a Straight connector.
The SATA power cable connector, and the SATA data cable connector; MAY have a Lock on top.
Usually a small depression, or Tab, or 'bulb'.
Depress with your thumb tip, to install, or remove the cable.
(Hmmm, betting now the P3 power cable may be a SATA power cable.
How'd I do? Post back in a Comment)
For additional questions please post in a Comment.