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I'm going to add a couple (3 to be exact) electrical circuits for my dashcam, USB power port and brake light relay (for when I'm towing behind my motorhome).


I bought the Add-a-circuit setups where you plug into a fuse slot and attach the new wire to it. I've done a lot of wiring on vehicles in the past but I'm not up on all the new computerized issues. I'm kinda old school, when I learned how to work on a car we still had to set the dwell and point gaps on the ignition!


I just want to know if there's anything I need to worry about so I don't blow up my electrical system. I had planned on adding the circuits to fuse slots that are controlled by the key (not hot all the time).
 

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The dash cam and the usb power port don't really need an "add-a-circuit" since you can take the power from a system which is already fused. On the back of the rear view mirror there is a plug-in which can supply power for the dash cam, and your 12 volt outlet power on the lower dash can be used for usb port


As for towing behind the motorhome.... Slide some diodes into the brake lights, running lights, on the jeep and then just use a standard trailer towing connection from the motorhome


None of these cases should interrupt the can-bus system in any way.
 

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I'll add to what Bob said and advise a good quality relay. Tyco makes some with low drop-out voltages that are appropriate. Cheap relays have high drop-out voltages and tend to release (chatter then burn) when fed pulsewidth modulated power with a duty cycle below their drop-out point.
 
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The CAN BUS is a communications network. Controller Area Network. It consists of 2 wires.

What it does is allow different devices within the vehicle to communicate with each other.

What the CAN BUS does not do:
- It does not provide power to devices.
- Individual components such as lights, switches, and electrical motors do NOT connect directly to the 2 wires of the CAN BUS.

To the point I make about lights above, I will use as an example to explain the CAN BUS further since many companies add confusion in regards to needing a "CAN BUS adapter" or "CAN BUS Resistor" for adding lights such as LEDs. These terms are technically incorrectly used because these adapters or resistors do not technically get connected to the 2 wires of the CAN BUS network.

If you have a basic understanding of electronic components and terms such as resistors, diodes, transistors, Load, resistance, etc then you'll be able to more easily understand how things work and how the CAN BUS comes into the equation.

There are multiple computer "modules" within the vehicle. These computer modules all get connected to the 2 wire network of the CAN BUS. Thus, they can all "communicate" with each other over the CAN BUS network.

The BCM (Body Control Module) is one of these modules. It is the module which controls and monitors signals which provide power to the actual lights in the vehicle. Within this module it will also have a micro-controller (ie CPU) as well as have transistor output driver circuits. Think of these transistor circuits as power control switches. These transistor circuits will feed the actual Power/Voltage to the "Loads" in the vehicle, ie things like your lights in the vehicle. These transistor circuits have some brains built into them and are able to detect how much load is connected across their output powering the actual lights. They therefore know if the circuit connected to them is OPEN, CLOSED, SHORTED, and the actual RESISTANCE of the LOAD connected to the output of the transistor circuit.

So let's say for example your left rear turn signal light burns out. When the light is working normally the transistor circuit knows the resistance should be around 2 ohms. When the light burns out, the transistor circuit detects there is now an OPEN circuit. The transistor reports this OPEN circuit state to the microcontroller in the BCM. The Microcontroller in the BCM then sends out a "Status Message" over the CAN BUS letting the other modules connected to the CAN BUS that may use this information that the rear turn signal is in an "OPEN" state. With that information now on the CAN BUS, further actions may take place by the BCM or other computer modules connected to the CAN bus. So for example, when you have a burned out turn signal, the light on your dash will rapidly blink to let you know the left turn signal is burned out/OPEN.

People run into this situation all the time when swapping their rear turn signals with LED lights. When doing that, you need to understand what are the differences between an incandescent light bulb and a LED light bulb. The incandescent light bulb in basic circuits is essentially a resistor. An LED light is a DIODE. A Diode in one direction is an "OPEN" circuit and in the other direction it is a "CLOSED" or Shorted Circuit. A diode is definitely not the same as a resistor to a circuit. So when doing a swap of lights like this, you are removing a resistor and replacing it with a diode. So what does the transistor circuit now see for the load across it? A diode is now connected across it so its either seeing an OPEN or CLOSE circuit instead of a RESISTOR. The transistor circuit then reports that OPEN/CLOSED circuit to the microcontroller, the microcontroller in the BCM reports that OPEN/CLOSED status over the CAN BUS. Then the action is the same as if you had a burned out turn signal because the load across the transistor is the same. Your turn signal rapidly blinks because the transistor circuit which powers the actual light thinks there is an open circuit across its output. So how do you trick the transistor circuit into thinking the circuit is not open when having a diode across it? You add one of these improperly named "CAN BUS RESISTORS" across the outputs of the transistor circuit to replace the actual incandescent light bulb you removed so the transistor circuit now detects the 2ohm load it is expecting to see across its output.

So if you understand those principles, then you can easily understand how the CAN BUS works within the "System". It's nothing more than a communications network. When you start connecting things to a fuse box, this same scenario applies. Typically if the impedance/resistance of the load you are connecting is high, then you likely won't run into a problem. If you understand basic ohm's law of calculating the total resistance of 2 resistors in parallel then you understand why that is the case. Connecting a 1 MegaOhm resistor across A 2ohm resistor in parallel, the 1M resistor will have very little impact to the TOTAL resistance/load across the circuit. Connect a 1 ohm resistor across that same 2ohm resistor, then the total resistance drops to .67 ohms. So now you're risking the transistor detecting that the total load is not within range of what it is expecting to see (ie 2ohms), the transistor will report that to a microcontroller, and the total resistance may be below a defined threshold and report it as a SHORT condition, and then the micro-controller reports that over the CAN BUS, and an action could take place. That action could be turning off that transistor circuit to protect itself from burning out.


Relays work as suggested above if you understand the basics of a relay. A relay gets connected across the outputs of the transistor circuit. The relay has a coil of wire with HIGH resistance. That coil of wire gets energized by the circuit, a magnetic field gets generated in that coil of wire, that magnetic field causes a switch to close within the relay, then the load is powered by the relay which is connected to power. I'm not a fan of relays but people tend to understand how they work so I won't knock them. There's better devices than relays such as MosFets and Transistors and if you ever seen a "Solid State Relay", that's what those devices are made from.
 

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That should be more of a sticky than the incorrect sticky we have now...
EDIT: that old sticky is gone. I didn't notice.
 

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Yeah, RednRoll covered a lot of it.

One of the big benefits of the CAN bus is that you can actually reduce the number of wires in the vehicle.

Take your power windows for example. And consider an ordinary car with the window switches in the door. Back in the day, there was a bundle of wires that had to run to the driver's door. That lets the driver individually control windows with a switch. And in some cases even disable the switches on other windows. Well, that took over a dozen wires to the switch and they had to be heavy gauge because they were running electric motors. And then you add the wires for the heated power mirrors and power locks and you had a ton of wire running all over the car.

In comes the CAN bus. It's basically just a computer network. So when they put the door together now, they just run one power wire into the door that supplies the window motor and the mirror. Then they run the two CAN bus wires into the door. They stop off at the power window switch unit, then jump to the window motor unit, stop off at the power lock module, and to the mirror unit. 3 wires run into the door. And two of them are pretty thin since they're just computer network.

When you hit the window switch, it sends a signal out on the CAN bus. The appropriate window motor detects the signal and activates the motor. Same thing with the mirror. Hit a button on the dash and it sends the command to turn on the mirror heater. Use the buttons to adjust the mirror and they just send signals to the mirror and tell it to do its thing.

Beyond that, you can move the switches anywhere. The Wrangler has the switches in the dash. It all still works the same way. It's tapped into the network, just in a different place. But everything still works the same way. There's no reason you can't put another switch in the door and have it work. Jeep decided that removable doors didn't need all of the switches in the doors adding weight to an already heavy door.

The car maker can even have a smart remote. Because everything is on the network, you can have your car remote do all sorts of things. Hit "lock" and it can roll up the windows while locking the doors. Hit unlock and it will move the seat (it's on the CAN bus), adjust the mirrors, the steering wheel, etc. all to the preset positions for the person with that remote. Hit unlock with the other remote and it will adjust everything for the other driver.


But the great thing is that doing an "Add-A-Circuit" keeps working the same way. Because all you are doing is adding a tap to the power, you're not bothering the CAN bus. You can still run your wire to your accessory and wire up the switch (and relay) the same way.
 

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Are you saying there is an unused power outlet on the back of the rear view mirror? How does that work with a USB powered dashcam?
I doubt there's an unused plug. But the power wire supplying the mirror can be tapped (it's just power after all) without affecting the CAN bus. Then you can run that tap over to the camera.
 

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That should be more of a sticky than the incorrect sticky we have now...
EDIT: that old sticky is gone. I didn't notice.

I started reading that sticky in the past...and got half way through and just shook my head, since there seemed more confusion added then what it solved. I decided not to jump in that thread but figured this was a good opportunity to try and assist for this thread. :drinks:
 

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Cannibus [ˈkanəbəs] - Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions.
 

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Cannibus [ˈkanəbəs] - Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions.

Also often used for networking communications. :D
 

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On the back of the rear view mirror there is a plug-in which can supply power for the dash cam, and your 12 volt outlet power on the lower dash can be used for usb port
Are you saying there is an unused power outlet on the back of the rear view mirror? How does that work with a USB powered dashcam?
I doubt there's an unused plug. But the power wire supplying the mirror can be tapped (it's just power after all) without affecting the CAN bus. Then you can run that tap over to the camera.

Keep in mind the rearview is switched power, only comes on when you turn the key.
If you are looking to use a dashcam that has a park mode it will need uninterrupted power, easy way is actually the ODBII port, there is constant power/ground provided in that port.
Many dashcam makers have an ODBII port adapter for this reason, and they know every vehicle on the road has one.
 

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I doubt there's an unused plug. But the power wire supplying the mirror can be tapped (it's just power after all) without affecting the CAN bus. Then you can run that tap over to the camera.

Curious to see if anyone’s gone this route and can comment on tapping the 12v mirror power and converting it to a micro USB adapter for the dashcam.
 

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This may be useful. The fuse box for the JK.




Now that we all understand the CAN BUS. :D This is how I supplied my Dash cams constant and ACC controlled power so they could be used for parking mode operation using fuse taps. I previously tapped into the ignition controlled cigarette outlet wires to turn my audio amplifiers on/off. I figured those outlets are designed to deliver 15 Amps of current and anything can be plugged into them, then that's a pretty good tap location.

M8 and M7 are ignition controlled. I had difficulty fitting a fuse tap into the M8 plugs and went with M7 instead.
 

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Curious to see if anyone’s gone this route and can comment on tapping the 12v mirror power and converting it to a micro USB adapter for the dashcam.
I ran a pair of 6 gauge wires off the battery to an aux fuse panel that I mounted under the glovebox. Gives me clean power for my variety of gizmos like radios, etc.
I ran a charge dock off that but you could run anything you want. Real easy to route wires up along the windshield.

Fuse the heck out of it though. And if you want it switched (I didn't), you can do that easily with a relay.
 

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Instead of trying to install diodes for the taillights, buy a Hopkins dinghy kit (or another brand). It plugs into both taillights and has a harness that runs to the front for the RV connection. Very simple, about an hour to install.
 

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Curious to see if anyone’s gone this route and can comment on tapping the 12v mirror power and converting it to a micro USB adapter for the dashcam.
Its going to more than just a little wire, anything USB is 5v.

There are a few ways to step down 12v to 5v but all require a component of some sort.
There are dashcams that run off 12v that won't need the voltage stepped down but more and more everything is USB, it is a nice easy standard and I am happy to see it used more and more.
You could gut a USB Cig light adapter and use that to get a usb port up at the rearview.
Just be sure to rewrap all the guts in some good heat shrink to keep them dry.
 

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Cannibus [ˈkanəbəs] - Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions.
This is one my mechanical engineer mind can relate to. :)
 
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