Originally posted by DennyW
You better re think your wire sizes. 18 is like telephone wire. Most automotive wire is at least 16ga. Alt bat wire should be at least a 12 ga.

Keep in mind also the different outter coating. What it is made of material wise. Some of that expense does seem a little high, but you are not just dealing with a bulk roll of wire. Neoprene coating, and high temp coatings all take a little more to process.

I think there is a couple more ways to do it, and manufacturers to deal with price wise.
18awg is good for a trustworthy 5A, and I would imagine that would be fine for a lot of the wiring(72W worth of pwr), such as interior lighting (assuming they are on thier own circuits). 16awg would be better, but if you do not need it, then no reason for paying extra if you're on a budget. 12awg for PWR and GRND is a little small, seeing as how it is only rated at 20A. 4awg is standard, but I always try to use 2 or 00awg.

The coating for most quality speaker wire should be fine. I ran my 4awg PWR through the engine compartment of a daily driver Tahoe in Sicily for 3 years and never had a problem

Although I am just going by my own experiences. What works fine for me may not work fine for others, right..