basic wiring question

I am planning on splicing some wires together and wanted to know a couple things.

What is the best way to tell what gauge a wire is (it is the wires going to the 12v cigarette adapter)?

Can I splice two wires together that are of different gauges (ex.  18 gauge and 20 gauge)?

What are the standard gauge wires used in a car for the stereo etc..?

Thanks 

Mark 

You CAN splice wires together of different sizes, but it's not the best idea, and you will lose some power handling capability when you go from larger to smaller. I dont have any proof but I think that it's generally a bad idea to splice from power source to smaller wire to a bigger wire, seems risky to me.

I think the wire gauge in your car depends on the manufacturer, but it's somewhere in the 18-24 range more than likely.

My experience has always been that it's probably best to just run a new wire if you can. Splicing is only 10% guaranteed, cause there's a lot of things that go wrong depending on how it's done. If i'm not mistakes, there are measurements on the site for wire sizes, check the power and ground area.