How-To Here's how to safely tap 12v power for add-ons

BigBri

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Okay straight to the point.. who in So.Ca. wants to help me install Blackvue for a nice bottle of your favorite beverage, Costco card, RPM gift card?:D
Seriously though I've had 2 new in box unwrapped 2 Ch 750s and have had appointment from professional installer who wanted $300 for install but right before install he told me I would have to buy the external battery at a cost of another $275! So after the entire expense I'm almost to $900 for a dash cam . Just not sure its that important .:(
Tap into the domelight if you don't wanna use an external battery. It's a 'risk' that you could need to replace the 12v battery if it starts throwing errors but I'm near 3 weeks strong without a problem on mine. Did my front and rear install in maybe an hour and a half. Most of that was just fiddling with the wires to get it together the way I wanted.
 

lairdb

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Have a look behind the right rear side carpet. That is where the subwoofer and amplifier is. There is a large red wire that should be switched power. Be sure to fuse your wire for what it needs. The amp circuit likely draws 30A or more.
Do you know of a trunk teardown anywhere? I want to get into the CHMSL harness, but I'd rather start with someone's video guide to pulling the trunk liners.
 

lairdb

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Tap into the domelight if you don't wanna use an external battery. It's a 'risk' that you could need to replace the 12v battery if it starts throwing errors but I'm near 3 weeks strong without a problem on mine. Did my front and rear install in maybe an hour and a half. Most of that was just fiddling with the wires to get it together the way I wanted.
There seems to be an increasing community consensus that wiring to the battery directly is what causes the current draw error, whereas wiring to post-ECU points (e.g. lighter, mirror assy, VCLEFT sunroof/trailer...) are accounted for in the current measurement accounting.
 

BigBri

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There seems to be an increasing community consensus that wiring to the battery directly is what causes the current draw error, whereas wiring to post-ECU points (e.g. lighter, mirror assy, VCLEFT sunroof/trailer...) are accounted for in the current measurement accounting.
Yeah it's logical to me. The extra draw from the battery confuses the car if it's not from a known accessory. The extra load seems to force the car to throw errors. I've had good success with mine so far. Range loss seems a smidge higher but within error margins.
 

garsh

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Yeah it's logical to me. The extra draw from the battery confuses the car if it's not from a known accessory.
You don't suppose that Tesla actually has an ammeter on every fused circuit?
If so, they could make sure that the total battery current equals the sum of all fused circuits, and throw a fault when they don't match.
 

Feathermerchant

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Well my 2011 F150 has a current sensor (hall effect device) on the negative battery cable. It is there for the truck to know the battery state.
If you add an accessory anywhere on the '+' side and to the frame or body on the '-' side you're OK. You just may not connect to the minus battery post without also going thru the sensor window.
 

BigBri

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You don't suppose that Tesla actually has an ammeter on every fused circuit?
If so, they could make sure that the total battery current equals the sum of all fused circuits, and throw a fault when they don't match.
So far I've not had any issues with my setup but hard to know in the long term. The 12V battery error wasn't super common. Few reports of it happening but some had no trouble wiring directly to the battery.
 

JWardell

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You don't suppose that Tesla actually has an ammeter on every fused circuit?
If so, they could make sure that the total battery current equals the sum of all fused circuits, and throw a fault when they don't match.
As there are no fuses, that means that yes, there is a current sensor on every circuit, so it knows when to shut them down. Though this might be a single chip instead of actively monitored by a micro, but knowing Tesla they did the latter.
 

teslamd

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Okay straight to the point.. who in So.Ca. wants to help me install Blackvue for a nice bottle of your favorite beverage, Costco card, RPM gift card?:D
Seriously though I've had 2 new in box unwrapped 2 Ch 750s and have had appointment from professional installer who wanted $300 for install but right before install he told me I would have to buy the external battery at a cost of another $275! So after the entire expense I'm almost to $900 for a dash cam . Just not sure its that important .:(
If you were in the Bay Area, I'd help you. It takes 30 min. Watch a few YouTube videos. Get the red positaps...
 

_Travis_

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For those of you looking for a nice switched 12v output for add-on accessories in your 3, I have found a good safe place to attach. See my YouTube video.

See the video's description for more details on this as well.

If you want a non-switched line for a dashcam, you can tap the yellow wire that feeds the overhead light/hazard switch console. The black wire on the opposite corner is ground.
Have you found a good way to pull out several tens of amps? I’m putting together a stereo that will pull 50-70W nominal, but >1kw peak. I’m wondering if I should wire to the 12V DC-DC directly, or if I should use the metered 12V you show with a capacitor or battery downstream with some sort of current limiter for startup.
 

eXntrc

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Have you found a good way to pull out several tens of amps? I’m putting together a stereo that will pull 50-70W nominal, but >1kw peak. I’m wondering if I should wire to the 12V DC-DC directly, or if I should use the metered 12V you show with a capacitor or battery downstream with some sort of current limiter for startup.
Hey @_Travis_ . You'll want to check out this thread:

https://teslaownersonline.com/threads/aftermarket-sound-system-info-thread.10022/
 

eXntrc

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Just curious if anyone else has had problems with the 12v pin connector @Ingineer showed in his videos? I finally got the radar detector installed last night using his method and I even went with the exact same 5mm spade connector he linked to on Amazon. I do get 12v switched from that port, but the spade just isn't making a solid connection. During install I even had it fall out! I did remove the plastic barrel from the spade connector so it could be inserted further and even tried to "tighten up" the spade much as possible with needle nose pliers.

I ended up adding heat-shrink tubing on the outside of the spade connector to increase its diameter and give it some holding friction. It seemed like a more snug fit, but even though it wasn't falling out anymore it still managed to lose connection while I was putting the vehicle back together. I light tug on the wire and power came back, but that feels very unreliable to me.

Looking back through this thread I see that rvandrew ran into a similar problem:

I fought for a long time to plug the wire onto the socket, even tried several different types of female spade connectors, to make sure I had a good fit. (...) Ideally, what I would like to do is get a similar mating female pin, put a wire on it (...) That way I could feel more confident in the connection onto that socket
@rvandrew did you ever find a better connector for that pin?

Anyone else that's been using this method, how has your connection been holding up? Have you ever had it drop out when going over a bump or rumble strip or anything?

Thanks!
 

TirianW

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...I ended up adding heat-shrink tubing on the outside of the spade connector to increase its diameter and give it some holding friction. It seemed like a more snug fit, but even though it wasn't falling out anymore it still managed to lose connection while I was putting the vehicle back together. I light tug on the wire and power came back, but that feels very unreliable to me.
...
The first three times I hooked up to that pin, I had the same issue as you with it coming loose. However, after taking everything apart for a fourth time, I got my inspection mirror out and was able to see that the spade lug was not going over the terminal but above or below it. Once I installed it correctly, it has been solid ever since. So I would get a good inspection mirror or borescope and double check it to make sure it is connected correctly.
 

Rbrooks84

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sorry for coming late to this thread but has anyone managed to do this and connect the 12v to a wireless charger? im getting one soon and want to have faster charging for my phone.
 

eXntrc

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I would get a good inspection mirror or borescope and double check it to make sure it is connected correctly.
Thanks Tirian. I ended up realizing that in an effort to tighten up the connection I had "over-compressed" the spade connector. I actually had to use a small screwdriver to slightly loosen up the inside of the connector a little bit and then I was able to get a solid connection. Hasn't dropped out on me since.

has anyone managed to do this and connect the 12v to a wireless charger? im getting one soon and want to have faster charging for my phone.
I have not attempted this, but I did end up buying the Nomad wireless charger especially designed for the M3. It really has no business being that expensive, but I mention it because it does provide up to 7.5 Watts per side (15 watts total) just using the M3 USB ports.
 

Achooo

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I tried to read through most of this very long thread and couldn't find an answer. I may have missed it, so I apologize if this has already been answered:

Whenever I've done any electrical work in years past on ICE vehicles, I have always disconnected the negative cable on the battery. Is there some similar precaution I should be taking on the Model 3 before attempting to access any switched power?

Thanks!
 

eXntrc

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The Model 3 doesn't have traditional fuses. If any one of the power lines are shorted or draw too many amps, a digital "breaker" trips. This breaker automatically resets, too. I don't know if the reset happens after a few seconds or if it requires a power cycle, but it eventually resets.

I have done the 12v power tap that's discussed in this thread for a radar detector and I didn't bother disconnecting anything. In fact, I don't know what you'd disconnect if you wanted to. You can take the terminal off the battery, but I believe the rest of the vehicle would still be connected to the 12v source coming from the penthouse.

I'd be interested to hear what anyone else has to say on the subject, but I personally don't think you need to do anything really before working on a 12v line. Of course you should take steps to avoid shorting it out, but worst case scenario just wait for the reset.
 

JWardell

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I tried to read through most of this very long thread and couldn't find an answer. I may have missed it, so I apologize if this has already been answered:

Whenever I've done any electrical work in years past on ICE vehicles, I have always disconnected the negative cable on the battery. Is there some similar precaution I should be taking on the Model 3 before attempting to access any switched power?

Thanks!
You can go into the service settings and power down the car to shut down the computers and nannies. Definitely recommended unless you're prepared for a bunch of errors because you inadvertently removed power from one of the computers...whoops
That doesn't actually remove 12v battery power, but that is not necessary if you are tapping a switched 12v connection.