You're likely thinking about a standard ATX power supply (SMPS) used in computers. In that case, there's no -12V wire.

Here's why:

* Modern Power Supplies: Most modern ATX power supplies (SMPS) no longer include a -12V rail. This is because older components that used -12V have become less common.

* Legacy Components: Some older motherboards and expansion cards might have used -12V, but this is rare in newer systems.

Instead of -12V, you'll find:

* +12V: This is the primary power rail for most components, including the CPU, GPU, and drives.

* +5V: Used by older components and sometimes the motherboard.

* +3.3V: Used by modern components, especially the motherboard.

* -5V: Very rare these days, used by some specialized components.

If you are working with an older system that needs -12V, you'll need to check the documentation for the specific power supply. However, in most cases, you won't find a -12V wire.