Could someone describe the amp meter scheme?

["K M" <symbiotic@hotmail.com>]

I am a bit confused about the wiring of this device.  As I understand, 
to detect the flow of current the meter is wired in line.  But this and 
most all the devices that I have seen used in cars are not wired this 
way -- it would be too hard to get the huge wire under the dash!  So I 
kinda figure that there must be some induction device somewhere that 
"sends" the reading to the gauge.  Am I way off base here?  Thanks, Kim.