This is a cut and paste from a post Bloozberry commented in about how to tell what gauge of wire is in the Fiero using the wiring diagrams in the Haynes or factory service manuals.

If you're building your own harness, then you really should get a manual which shows you the size of the wires used in the stock configuration. While some people use just any old wire they can come across, the gauge of the wire is chosen to support the amount of electrical current (amperage) of the total current draw on any given branch of a circuit. If you over-size the wire, there aren't any problems except that it's harder to work with and can add more than a few pounds to your car. If you under-size the wire, you risk melting the insulation and having shorts and even fires.

Here's an example of a typical wire diagram:

The number just before the color of the wire (for example "1 ORN" at the top) indicates the gauge of the wire that's used in metric. A 1.0 is equivalent to 16 AWG. All of the wire diagrams show several different wire gauges throughout. You can't always judge the gauge of the wire by looking at it's outside diameter since different insulation materials and thicknesses are often used. If it helps, here is a conversion chart from metric to AWG sizes:

Metric / AWG

0.22 / 24
0.35 / 22
0.5 / 20
0.8 / 18
1.0 / 16
2.0 / 14
3.0 / 12
5.0 / 10
8.0 / 8
13.0 / 6
19.0 / 4
32.0 / 2

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Some helpful links I've done
How to remove inner door panels, with pics.
How to remove outer door panels, with pics.
How to make rear coil-overs using factory struts, with pics.
How to remove rear bearing hubs, with pics.
How to modify the stock Fiero radio for MP3 players, with pics.
How to come up with the right coolant hoses for that engine swap...With Pics.
Basic Fiero electrical testing "How To" and equipment...with pics.