I'm in the process of wiring my car for an LS1 swap. I have a lot of wires to lengthen and shorten.

I'm horrible at guessing the wire size. I know the insulation throws a variable in the mix, so it's difficult to find a chart with insulated OD, and that the correct way is to cut the wire and count/measure the strands.

I have all the GM schematics that list the wire sizes. For examples...
5 PPL for the starter sol
3 RED for the fans
1 GRY for the f/p
.8 BLK for a ground
.5 ORN for PCM power
.35 BRN for the MIL light

What do these numbers equate to?
Is it just the metric equivalent?
Based on this chart...
https://en.wikipedia.org/wiki/American_wire_gauge

5 = 4 ga
3 = 8 ga
1 = 10 ga
.8 = 12 ga
.5 = 16 ga
.35 = 19 ga

 

You are correct. The #s GM gives are metric. However, you used that table incorrectly; you should be looking those up in the Area column, not the Diameter.

You can however measure the dia of a wire that you have, and look up in that column to find the gauge.

So, 5 mm˛ (not mm) is more or less equivalent to 10 ga.; 3 mm˛ is close to 12 ga; and so forth.

I would NOT run any wire smaller than about 14 ga for a fuel pump... too much voltage drop on account of the current demand of those.

You'll find that good quality wire is worth every penny. Besides just the gauge (copper diameter) the insulation is CRITICAL. DON'T buy the crap at AZ and the like; it's insulated with PVC (vinyl) which melts. Good-quality wire has neoprene, XLPE, hypalon, etc. instead. High-temp stuff that will last under the conditions found around an engine.

https://4rcustomswire.com/products
http://www.wireandsupply.com/
http://www.texasindustrialelectric.com/
http://www.wiringproducts.com/

 

This chart is right out of the GM Service Manual.

 

Thanks. I thought it looked a little off. And thanks for the rest of the advice.

That's the money shot! Thank you!