When not plugged into 12v, the light only comes on when you press the big
round "light" button.  Stays on a few seconds, then turns off.  As someone
else noted, and I have observed, the temp reading varies slightly on 12v vs
battery power.
Edward

At 07:39 PM 4/21/2005, you wrote:
>Entity Jonathan Farrugia uttered this profundity:
>
> > all the stores in close distance to my house showed them but there was
> > only the one on the shelf at the closest store, which i bought :).
> > i don't know if > it stated in the web description but it runs on either
> > two AAA batteries or 12 volts, to run the temperature functions that is.
> > i had wondered about it being a parasitic drain on the system.
>
>  Cease thy wonderment! I measure it at 27 mA per hour, which is .648 amp per
>day. Hardly significant for daily driving.
>I notice the backlight is on all the time when the unit is on 12v. Pretty
>good idea. I wonder if I put batteries in it if it would only show the
>backlight when it has external 12v? Anyone?
>
>-- Gnarlie