This is strange, at least to me - even with the car off, key out of ignition, I'm measuring 12v to chassis ground across ALL of the ATP mini fuses. Is the ground controlled by a relay? Things have certainly changed since the 70's!

 

Welcome to newer vehicles..... You could have a relay or Field Effect transistor that is being kept alive by a body module until the body module goes to sleep [ industry talk for an ECU /Module finally shuts down after a nominal time spec, usually 15-20 minutes max.
You could have a Battery hardwire connection to the fusebox that is always hot, but is not USED in terms of consumed amerage downstream of the fuses by control modules unless they're awake, so no real drain on the battery to speak of[ 50 milliamp drain is usual industry standard that they shoot for with key OFF and all ECUs asleep].
That last paragraph is how most European vehicles that I see are set-up.
Battery Cable to any of the fuseboxes[ there are often 3 or more in the vehicle] and either no control of the fuse power out of the Fusebox to where it's routed, OR, there is a relay or Field Effect Transistor inside the fusebox that is controlled by which ever Module is designed to run it, giving power to the fuse only as designed by the engineers when they want it to power up a circuit.
Another way to look at it is that some Battery Hot fuses will feed the 'Memory' power to a Module, in tiny amounts of power even with your ignition key off, but once that module is awake and running, then it in turn controls many more fuses in the fusebox and your power consumption then goes up dramatically.

 

Thank you Pure Red, that's what I was afraid I was going to hear.

So, what do you think about the main 12v power outlet? Is there any chance that I'll be able to use that fuse? Or, should I just use one of the others in the "hope" that my dash cam won't drain the battery before it goes to sleepy time?

 

Why don't you wait 20 minutes and then check power on the fuses? Dash cams draw very little power. I'd imagine they could run 24/7 for weeks without draining the 12V battery.

 

Don't know for sure how BMW or MINI works their lighter fuses on your car. In the past BMW would from my experience leave the lighter fuse always hot, so leaving something in it would drain the battery. But they might route the lighter through a module these days like other car makers, so test yours to see which way it works.
Give me your vehicle year and model and I'll try to look up the wiring diagram to find an Ignition Only fuse that would power down with the key off, allowing you to tap into it for your Dash Cam

 

In 1st generation MINI, the lighter fuse is switched (tied to the ignition).

Here's the wiring diagram for R57: https://www.newtis.info/tisv2/a/en/r...s-cab/6qVQmvxB
Lighter is on F44 and there's a relay in the path, but I can't find what I01069 is connected to.


Edit — found it. I01069 is connected to the "Car access system":
https://www.newtis.info/tisv2/a/en/r...ronics/btYupoC
https://www.newtis.info/tisv2/a/en/r...s-cab/CkNG9jP0
https://www.newtis.info/tisv2/a/en/r...-s-cab/ZItKoZh
The function of the wire (from pin 8 on X10318) is not described, but I would infer that it has something to do with the car being turned on.

 

Oh man, I'm getting in over my head LOL.. If Fuse 44 is the one I need, that might be a problem because it's very close to the fuse compartment cover and the piggy-back Add a Fuse might not fit.

Update: Fuse 44 looks like it would work, but it's definitely too close to the cover to use the Add-a-Fuse. Is there any device that is similar but a lower profile? You can see how close it is to the top in the photo - 5th one down in the right most bank (20A)

 

Thank you - it's a 2011 Mini Cooper S convertible. I believe it's an R57

 

Would this work?

https://www.rdforum.org/index.php?threads/21410/

Scroll down to find a brass strip from Advance Auto Parts - it looks like you could bend the connector down at 90degrees.

 

Yes, thank you! - this may work :-) A Dorman Fuse Tap.... Advance sells them for $2 but not in the store. I'm going to see if they'll order a few for me.