add a circuit fuse tap / auto dim mirror

I bought an add-a-circuit tap thing to source power for an auto-dimming rear view mirror, but how exactly will it work when in place? Will the mirror be on/powered all the time (like power seats or power door locks), or only when the car is running? Or does that depend on which of the fuses I tap for power? Also... The interior fuse box HAS a listing for a factory installed dimming mirror but it's on the same fuse/circuit as a whole load of other stuff. I was thinking it might be best to tap a fuse with less junk running through it? Both the Cigar Lighter (30amp) and Heated Mirrors (10amp) have their own fuses, nothing else on with them, so would it be better to use one of those rather than the factory location? I really don't want to pull the fuse for the factory location even once as it's the same fuse that controls the EATC climate control, which will cycle through calibration every time the fuse is removed.

Not sure it's relevant, but the car I'm adding the mirror to is a 1994 Lincoln Town Car.

If the cigar lighter isn't constant, that ia ACC or IGN. controlled that's fine but really should you be even attempting this from your line of questioning? Those fuse adding devices don't affect the original load, they're in parallel with their own fuse.

Tap a fuse that only has power when the car is on/running. Having it constantly powered is a needless drain on the battery that could lead to a car that won't start (dead battery). No one really needs the mirror to auto-dim when they aren't driving the car.

howie ll wrote: If the cigar lighter isn't constant, that ia ACC or IGN. controlled that's fine but really should you be even attempting this from your line of questioning? Those fuse adding devices don't affect the original load, they're in parallel with their own fuse.

Well, I know HOW to do it, it's just the little details I need to work out before I start. I want to set it up the right way the first time.

catback wrote: Tap a fuse that only has power when the car is on/running. Having it constantly powered is a needless drain on the battery that could lead to a car that won't start (dead battery). No one really needs the mirror to auto-dim when they aren't driving the car.

Yes, exactly my thinking as well.

As in ACC or IGN. TEST.