Larry,
It is possible to do it, but it would be weird and complex. As
suggested already, you could use both the line-level and speaker-level
outputs of the head unit; line while driving and speaker while parked.
It would be very easy to put a power switch on the "switched power"
lead that comes off the head unit and signals the amp to turn on. The
main gotcha is that you'd have to absolutely interrupt the
speaker-level outputs when the amp is on. Easy enough: on/off switches
for each wire, or a switch that has multiple circuits built in to
handle maybe up to four leads at once.
Do you really need every single speaker active when you're parked? If
you only used one pair, there would be fewer wires to switch on/off...
-Simon

On Saturday, November 9, 2002, at 09:14  AM, Larry Chase wrote:
>
> One of the goals I had in mind was to have a small external power amp.
>
> The idea was to use the external amp while driving and to turn it off
> and just use the head unit's internal amp when camping.
>
> The reason being to minimize power consumption when camping.