Wire size

["William M. Gilroy" <wmgilroy@lucent.com>]

Since I might be installing an electric fuel pump in my Midget (LBC
content)
I have a general electrical question. How do I decide what is the
correct gage wire for a given device?  The head lights need a much
bigger wire then a radio.  I mean given the amperage of a device
and the length of the wire run what would be the correct gauge
wire.  Sort of like 

        gauge = length/2 + amp/4 

You get the idea.  Most likely I will use a fairly thick wire
that I have in the rats nest box.  Also does it matter if the
wire is a solid core or stranded?

Thanks

Bill Gilroy
77 Midget
90 Shar-Pei