2015 Highlander: Acc Power in Map Light Cluster

I'm trying to get 12V acc power for my Passport 9500CXi and dash camera - which will both be located just beneath the rearview mirror.

The mirror itself has a 6-pin (or there abouts) harness, but only two wires - which power up only with the ignition on. Ultimately, I'd use that if I can't find accessory, but I'd prefer to have the camera running when in accessory mode.

There are two harnesses behind the map light cluster - one going to the cluster itself, and the other seems to be a simple junction between two bundles going through the space directly behind the cluster.   I've metered all the pins and found only two that are true battery voltage - but they're constant.

Does anyone have a good idea if ACC power exists above the headliner already, or do I have to run a cable up from the fuse box?

Not that I know your vehicle, but it's rare for ACC or IGN to be carried rearward. Exceptions include vehicles with rear cig-sockets or other power takeoffs, and some trailer plug wiring. Roof mounted amplified antennas may also have a +12V feed.

I'd consider using IGN as well to prevent camera dropout during cranking unless the camera has an off delay. Hence diode isolation of both ACC & IGN supplies - maybe thru a relay if the ~0.7V or ~0.3V Schottky diode drop proves to be a problem.

I run a cable pair for such situations (ie both +12V & GND) - usually fig-8 or coax - and terminate conveniently up front for easy switching options eg IGN & ACC, constant/manual, off.

Yeah, I'm thinking that's ultimately what I'll have to do. This Highlander replaces a '13 BWM X5 - which was a nightmare in its own right to find ACC power - but it was up there. The map light cluster, which includes the door-open-lights-on switch and homelink buttons, probably has some ACC power. I just don't want to smoke a 3 day old car and flub the warranty.

The dash cam (Blackvue) has a battery backup that holds over a drop in acc power for a few seconds during cranking. I think it takes upwards of 15 seconds to finish writing the current file and shut down after power has been cut.

At least the Highlander is Jap which IMO have always had superior electrics (since the 1960s).

Cams can be like GPS whereby they sense voltage changes - ie, switch off with engine off (no charging) despite still being +12V connected. [My cig sockets are constant +12V but my GPS & cameras still turn off with IGN off (when set to do so obviously).]

Not that I've investigated, but IMO it should be obvious that they have a short ride-thru delay to prevent power cycling during cranking and short term voltage sags. Without that they are very likely to hang - especially if it takes seconds to write files etc. (GPS shouldn't have that issue unless recording so it's only the usual requirement for a long enough break for CPU circuits).   


I didn't think of dome and map lights. D'oh! Traditionally they are constant +12V with GND switching to doors and on/off switches so they might be suitable sources - especially if they have voltage sensing as described above and no other switching requirements (eg, manual on). Alas these days they may use local GNDs with +12V switching.   

Years ago some used to multiplex existing wires - eg, use speaker wires for +12V transmission (with capacitor isolation for the speakers).
Signalling could also used - ie, inject an AC signal that controlled devices at far end. That became easier with later comms & uPC chips.
However these days, with BCMs & who knows what OEM equipment - it's no longer as simple as a naive add-on.

Tho running new wires is a PITA it is usually the most desirable.
When I go to that trouble I usually run extra wires (future proofing). Often it's a relatively hefty battery +12V with a few signal wires to control relays etc tho sometimes I might include IGN or ACC for simplicity. I often include a GND power wire for chassis independence. A lack of enough signal wires can be overcome using signaling & control techniques - eg PICAXEs and i2c comms or commercial 2 wire control systems.
More recently, cheap wireless remotes can be a great substitute for signal wires, or a great way to control any accessory. (I recently built a 50A Anderson connector intercept box that uses a 60A relay and wireless remote. Mainly intended for my 12V tyre pump but can be used for anything.)