I've always been curious about the "myth" that: A majority of cars have a stock amp burried somewhere in their dash; not built in to their stock head unit. Is this true? Is there a general set of manufacturers that do this? And... why would they?

The only stock radio I know is my 2000 Volvo one. It was a double din and sure seemed to have the amp built in to it. So I wonder, if the vast majority of aftermarket headunits can have amps inside, then why don't stock head units do the same? Wouldn't it be more costly to include an external amp in a stock car?

And it all boils down to: How can an empeg be powered by this mythical burried amp WHILE the stock headunit is out? Does the wiring harnass accept line-level outputs that go to the amp (as opposed to my notion that it accepts speaker-level outputs that go straight to the speakers)?

I may be helping my friend put his new dual-sled empeg into a Lincoln and a Geo (fun combo, eh?) which both supposedly have the mythical amp.