kenchan

if you have a voltmeter you can put your (+) probe on the bare metal you see on the top of the fuses (pict above) and your (-) probe on any metal ground and measure power while your car is in the ignition acc/on and off positions.

if you measure 12v+ at off, you got constant voltage... unless you want to charge your phone or something while the car is off dont use this. it can drain your battery if done too often.

if you get 0v at off and 12v at acc and on positions you got a 'switched' fuse. you
want to put your add-a-circuit on that fuse.

add-a-circuit can only handle up to 10A. so if you are going to pull more then that
you should pull directly from your battery.

btw, for radar detectors, i just tap directly into the fuse leg and not even use those add-a-circuit.
i put a 1A fuse in series somewhere. (just soldered on the wire) unless my detector comes with a hardwire harness (like V1).