Electrically inclined Wise Ones (David B?),

During a recent camping trip it was cool and very still outside, with lots
of mosquitos, but still warm inside the camper.  Opening the windows and
poptop screen did little to cool things off because of the lack of wind.  In
desperation i turn the ignition on, but did not start the motor, and was
then able to use the regular Heater blower to pull fresh air in. It cooled
us down in abouit ten minutes.

But, I don't really like turning on the ignition for this.  I want to make
the heater blower accessible without the ignition key in.  i know the heater
runs off fuse 10 .  how do I safely change this situation.

And where in the circuit do I put a switch to revert the system to stock
when not camping so I don't run down my battery by leaving the blower on
when I get home from work...

TIA for all wisdom
--
Miguel