I find this puzzling, I 'm changing the bulbs in the overhead console and decided to run wiring for a future dashcam installation while I have the console down. The wiring diagram shows several switched fuses (I) in the passenger-side fuse box, but when I went to confirm they're not energized when the key is removed, they all read 1.3V instead of 0.0V. The switched fuses on the driver-side, which are all (II), read 0.0V.
Does this somehow make sense?

 

Have you tried pulling the relay for those fuses and checking the voltage? You could also swap a relay to see if the problem goes away.

Next thing to try is to pull each fuse in turn to see if one of them is backfeeding the 1.3v from somewhere else - eg the radio.

 

Great troubleshooting advise, as always!

- Pulled the relay => all (I) still read 1.3V
- Pulled F10 (phone) => 1.3V
- Pulled F12 (head unit) => 1.7V
- Pulled F14 (cigar lighter) => 0.0V (aha!)
- Pulled F16 (Nav Display) => 1.9V

I have a USB adapter in the cigar lighter, not connected to anything at the moment, and when I remove it, the fuses read 0.0V.
Since the lighter socket, the Nav Display, and the head unit all affect the voltage some, albeit differently, I'm guessing this is what you electrical geniuses refer to to as phantom voltages and isn't anything I should worry about?
Thanks!

 

I assume the USB adapter has a smoothing capacitor in it and this is slowly discharging giving that small reading on your multimeter. It's nothing to worry about, but I would never have guessed it was the source of your reading, so well done for tracking it down.

This is one of the reasons that test bulbs are often more useful than a multimeter as they actually put a small load on the circuit. Eg something like this:-

https://www.ebay.co.uk/itm/305155052432

 

Without knowing which fuses and referring to the diagram I cannot be sure but be aware ..
1/ digital meters are not designed for use on cars due to there very high resistance and can give misleading readings. If you have an old fashioned meter with a needle try that for reliable results or even a small bulb
2./ circuits can be switched in the live or earth side and in our cars switched in the earth by MOSFETS in the ECU

 

Yeah, a test light like dibbit suggested would have been better in this case since the stray voltage would not have energized the bulb.
I've been using this one for most of the testing I've had to do. The ability to energize a circuit with the tip has been very useful.