Installing dash cam behind rear view mirror?

If you don’t mind my asking, where did you find 5 volts? Other than the USB connector in the console, I wasn’t aware of any 5-volt sources exposed outside of individual ECUs.

 

Thanks for the explanation, and now I understand why I didn’t remember it from the Electrical Wiring Diagram: that’s a dedicated power supply for the microphone in the Map Light Assembly, used by the navigation and Safety Connect systems.

The Repair Manual says (under Audio / Visual / Telematics: NAVIGATION / MULTI INFO DISPLAY: NAVIGATION SYSTEM: Microphone Circuit between Microphone and Navigation Receiver Assembly) that the red wire (O2-1 or O4-17) is the “Microphone power supply,” which should have 4 to 6 V, switched with ACC; this is provided by the Navigation Receiver Assembly, or if your car has Safety Connect, the Telematics Transceiver.

I don’t know, however, how much current this circuit was designed to provide, and I’m not sure I would connect an additional load, for fear of causing a malfunction or perhaps even damaging the Navigation Receiver Assembly or Telematics Transceiver.

The white and black wires (O2-4 or O4-15 and O2-2 or O4-16) are the ”Microphone voice signal,” and I would be hesitant to tap into them, especially since Toyota used a shielded cable, suggesting that it’s necessary to keep electrical noise out of this circuit.

 

I had my dash cam hooked up to the light fixture over a year ago with no negative issues.

 

I’m sorry not to have posted this in time for it to be of use to you, but for other readers, there is switched 12-volt power above the headlining, but it’s controlled by the DOME CUT relay, which acts after a 20-minute delay, not the IG or ACC relays. As the Repair Manual explains:

The main body ECU (multiplex network body ECU) controls operation of the DOME CUT relay in order to supply power to the interior lights. When the battery saving function operates while the interior lights are on, the main body ECU (multiplex network body ECU) opens the DOME CUT relay to turn off the lights.​

The Electrical Wiring Diagram shows the connections. Interior lights are supplied through the 7.5 ampere DOME fuse, which feeds the DOME CUT relay, which feeds (among others) positions 12–22 on junction connector O16; positions 1–11 on this connector are wired to ground point FA. Connector O16 is above the headlining, to the left of the opening for the map light assembly; on my car, the connector housing is made of black plastic. The housing has part number 90980-12B54, so new terminals could be added to the open positions using repair wires, part number 82998-24290 (0.64 II series), or with Sumitomo TS 025 terminals crimped to your own wires.

Of course, I’d suggest doing a load study before deciding to connect new loads to the DOME circuit, but since the existing load consists of lamps with known wattages, this wouldn’t be difficult.

 

As far as I know, the maximum current isn’t published; proprietary design information like this isn’t needed or useful for repair, so it’s unlikely to be available from Toyota or its suppliers, who if asked would probably just refer you to the general warning against modifications in the Owner’s Manual.

It would be challenging to determine a value through reverse engineering, without knowing the design criteria, such as the worst-case undervoltage on the 12-volt bus. You would also need to consider what else is powered from the 5-volt supply and its behavior in case of an overload: does it just shut down and then restart, or are there internal fuses or other components that would fail permanently?

 

Yes; on my car, connector O16 is mounted to the headlining with a plastic clip, just to the left of the opening for the map light assembly.

It’s black, not natural, but otherwise the same as this connector sold by hi-1000.com. (I’ve bought from that store, by the way—a small company in Osaka with parts that are otherwise tricky to find in small quantities. My order was carefully packaged and delivered quickly by Japan Post EMS.) You can also see part number 6098-3925 on page A-05 of Sumitomo’s Connectors for Automobiles catalog (12.8 MB PDF).

It’s a 22-position connector, but there are vacant positions on both rows (12 volts and ground). I encourage you to subscribe to techinfo.toyota.com ($15 for two days) to see the Electrical Wiring Diagram for your Prius, but the European left-hand drive version is very similar; see pages 4 and 8 for O16.

The DOME circuit and DOME CUT relay are for the interior lights. The Owner’s Manual says:

• Illuminated entry system: The lights automatically turn on/off according to power switch mode, the presence of the electronic key, whether the doors are locked/unlocked, and whether the doors are opened/closed.
• If the interior lights remain on when the power switch is turned off, the light will go off automatically after 20 minutes.

Here are a few more tips to consider:

• Measure the current used by your dashcam when it’s powered by an AC adapter or bench supply, and then figure the total current for all the other lamps on the DOME circuit. If the dashcam plus the lamps exceeds 70% of the fuse rating (7.5 A × 70% ≈ 5.3 A), use a different circuit or add a new one.

• Loads on the DOME circuit, rather than circuits fed from one of the IG relays, are part of the parasitic drain on the auxiliary (12-volt) battery, if only for a few minutes. It’s hard to give specific advice without design information Toyota doesn’t publish, but it would be good if your dashcam has a battery-saving feature, so if the battery voltage is low, it will turn off automatically.

• Rather than tapping into existing wires, use the Toyota repair wires (pigtails) I mentioned earlier to add new terminals to the connector, so you can remove everything later, if necessary, leaving the factory wiring harnesses intact. The current Electrical Wiring Diagram is the best source, but this 2007 edition of the Wire Harness Repair Manual (8 MB PDF) explains how to handle the connectors.

Note: I don’t know the details of your added load, nor your skills as a technician, so consider the above as general information, not an engineering design. I recommend against modifying your Prius at all, except perhaps by installing Genuine Toyota Accessories.

 

You’re most welcome.

Alas, no—the electronics controlling the hybrid system operate on 12-volt power, which is available only from the auxiliary (12-volt) battery until the hybrid system is started.

 

Just run the wire up from the fuse box. I monkey around looking for that 12v ignition on about a year ago and couldn't find it so I gave up. Running the wire up only took me 5 mins.

 

Do you have the powered auto dim mirror pre-installed on your car? I don't think the plug/wire is there if the car doesn't have the auto dimming mirror (as in my case). I pulled the overhead console out and there isn't one that I can see.