12V source in trunk in 2021 Model 3 without amp

[stopcrazypp]

I'm trying to look for a 12V source in the back (can be switched or unswitched) that can be tapped into. Did a search and didn't find anything, only sources for those with the subwoofer and amp, but mine is a SR+.

Was able to do trailer harness according to this thread, but looking for another 12V source that is not intermittent for something else, without having to run a cable from the cabin. I figured with so many wires to the back there has to be some source, especially given I have a factory powered trunk.
Build your own plug and play trailer harness!

 

[rotarypower101]

Trailer brake controller possibly, based on the link? If so, they make a 5 pin trailer plug variant that will allow normal 4 wire compatibility as well as allow a extra 12v pin for the controller.

 

[stopcrazypp]

Trailer brake controller possibly, based on the link? If so, they make a 5 pin trailer plug variant that will allow normal 4 wire compatibility as well as allow a extra 12v pin for the controller.

I'm actually using both for a security camera system in the car that currently is powered by 12V LFP batteries in the trunk, not for a trailer.

The trailer harness I'm using as a remote trigger to remotely reset the system when there are connectivity issues or some cameras overheated (the flashing of the taillight from the Tesla app triggers a relay that would momentarily disconnect the power source to the system). The instructions from that thread were easy to follow, and it was pretty much plug and play (the factory taillight socket and cable in my 2021 actually is now a custom Delphi connector, but the Tyco one is still compatible and plugs right in). Unfortunately none of the connections on the taillight cable has a constant source (they only turn on when you activate the given light).

I'm trying to add a 12V source from the car to use as backup for times when the LFPs run out of power. Even if it is a switched 12V source (which turns off when car is asleep), I can keep it alive with Sentry mode and have it running simultaneously.

The main reason I don't use Sentry mode instead by default is it drains too much power. My whole system only draws 7W for 4 cameras and a router, while Sentry uses about 1 mile per hour (which calculates to be about 210W, a whopping 30x the amount of power). Also Sentry seems less reliable in detecting events, and the FOV is worse in the front.

If there is some 12V source in the trunk I can tap into, I could keep everything 12V related neatly in the trunk without having to run an extra 12V wire from the center console.

 

[android04]

You can tap into the 12v output from the DC to DC converter under the rear passenger seat. It's right under the right passenger seat cushion and you can use a ring connector to connect to the positive post. A lot of people use it for aftermarket sound systems and it's easy to pass a cable from there to the trunk by going under the right rear part of the seat bolster.

 

[stopcrazypp]

You can tap into the 12v output from the DC to DC converter under the rear passenger seat. It's right under the right passenger seat cushion and you can use a ring connector to connect to the positive post. A lot of people use it for aftermarket sound systems and it's easy to pass a cable from there to the trunk by going under the right rear part of the seat bolster.

Thanks for the tip, I will check it out.

 

[davewill]

You can tap into the 12v output from the DC to DC converter under the rear passenger seat. It's right under the right passenger seat cushion and you can use a ring connector to connect to the positive post. A lot of people use it for aftermarket sound systems and it's easy to pass a cable from there to the trunk by going under the right rear part of the seat bolster.

Be sure to fuse that connection appropriately.

 

[stopcrazypp]

I did a bit more research on this and it seems the 12V post under the back seat goes directly to the PCS and has no protection from the virtual fusebox mosfets in the Model 3. That means if it is shorted by accident to ground, it will directly burn the fuse in the PCS, which is an expensive fix (instead of just a mosfet tripping and in worse case requiring a full hard reset).
How-To - Here's how to safely tap 12v power for add-ons

Given this, it's much safer to tap other sources. Found from a video that actually in footwell there is a 12V source that is always on which can be connected to with ring terminals, without needing to tap into dome light. In sleep, supposedly that drops to 9V, but that is ok with me as I already use a DC to USB converter that can tolerate down to 8V to power my cameras/router. If it really works this way, I may even save on needing to use my LFP batteries.

 

[stopcrazypp]

I did a bit more research on this and it seems the 12V post under the back seat goes directly to the PCS and has no protection from the virtual fusebox mosfets in the Model 3. That means if it is shorted by accident to ground, it will directly burn the fuse in the PCS, which is an expensive fix (instead of just a mosfet tripping and in worse case requiring a full hard reset).
How-To - Here's how to safely tap 12v power for add-ons

Given this, it's much safer to tap other sources. Found from a video that actually in footwell there is a 12V source that is always on which can be connected to with ring terminals, without needing to tap into dome light. In sleep, supposedly that drops to 9V, but that is ok with me as I already use a DC to USB converter that can tolerate down to 8V to power my cameras/router. If it really works this way, I may even save on needing to use my LFP batteries.

For what it's worth, the 2021 Model 3 is different and no longer has the screw terminals which you can attach a ring terminal to. I checked both driver's and passenger side. I apparently have the 1567455-02-D version which is newer and uses a power terminal that plugs in instead. I also tested using an OBD2 adapter under the rear of the console and the power is shut off when car is asleep (unlike others with older 2018 models that claim an update somewhere in 2021-2022 made it so it's kept alive).

Now I'm still trying to find some place to tap power lower in the car.