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Old 06-23-2010, 07:48 AM   #1
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Anyone wanna try to explain CAN bus?

The stealership has the Mopar / Hella Off-Road light kit with windshield mounts on order to do a "factory" install to become included in my warranty, supposedly. I know nothing about this mysterious CanBus electrical system and all I have been able to determine is that it makes add-ons challenging at best to a backyard wrench, and I would likely not learn enough to confidently install those OR lights myself anytime soon. Beyond the mystery, is there some overwhelming advantage over standard fuse-type systems? It appears to me to be a way to insure the aftermarket stuff can't muscle in on the OEM accessories, and that pricey stealerships and their pricey mechanics have to do the lion's share of the labor. Yes, we are in the computer-age, I get that, and the multi-computer car components need to work together seamlessly. But aren't we overcomplicating the big picture? To cut it off, what challenges await me to connect a cb radio or other electrical widgets?

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Old 06-23-2010, 08:31 AM   #2
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You would only have issues if you wired into the system. I've successfully wired two separate light system with their own relays and switches. It is independent of the CAN bus.

If you wanted to add fog lights that used the same factory switch as your factory fogs, then you would run into issues. Your windshield mounted lights will have to have their own switch since they can't be used on the road.

There is nothing difficult about wiring your own lights on the JK. They have even provided easy pass through to the engine bay. I would say that the most time consuming aspect of wiring my own lights was enclosing the wires in a loom so that it looked "clean".

Google can easily get you explanations of how the CAN bus system works.

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Old 06-23-2010, 09:39 AM   #3
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Old 06-23-2010, 01:30 PM   #4
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Without knowing too much about it, I would say that any system that has a standard current draw that is monitored via the computer and informs the driver when such things as a blinker or running light are out will be messed up when wired into for accessory lights. Adding a relay coil has minimum additional draw and putting the lights wired directly from the battery but having the relay switch in line which means that whenever the relay is on the lights will be on is a way of wiring and not affecting the computer controls in a negative way.
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Old 06-23-2010, 10:41 PM   #5
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I've successfully wired two separate light system with their own relays and switches. It is independent of the CAN bus
This is a dumb question but where do you tap in? I can see running the wires back to the switch (likely mounted in the dash) but then where do you take the wores to get power? Straight to the battery? To the fuse box?
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Old 06-23-2010, 11:09 PM   #6
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That's just it - there is no fuse box per se. Some engineer-types compare it to "USB" computer connections, only it is two wires (one high voltage like 11 volts, the other low voltage like 2 volts) but not the standard positive & negative terminals we think of in our old-school toys. Tinkering with the wiring to add stuff onto an existing "circuit" causes some voltage flux and even minor changes can really interrupt the whole system. So I'm told, and how do you tap a widget with pos & neg wires into a high/low voltage wire set-up anyway? The info to research is mostly highly technical and a bit intimidating to grasp. For instance: is there or isn't there an alternator or charging system as on other vehicles? Or if it is there it works differently and/or is called something different as well. I was hoping one of the electrical gurus would translate all the complicated techno-speak and give a simplified explanation of the jeep's electrical junk. What I have come to understand is this overall "grey area" is why the vast majority of JK owners add stuff via direct connection to the battery with a new and seperate switch to run each gadget. PITA I say! Great for the fancy-pants Beemer & Benz crowd, but really for a jeep? Perhaps the 2011 jeeps will have a glass cockpit and say good-bye to the standard guage cluster!
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Old 06-23-2010, 11:15 PM   #7
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I feel your pain in this post. I just spent three plus hours today mounting and wiring windshield lights on my Sahara. Removed wipers, wiper valance and went at it. A real pain in the a$$. No new scratches that I know of. However I am stumped on finding my in cabin relay power. Right now I am tapped into the fuse box. Everything else keeps the LED toggle lit up. Looking for a power source that is on/off with the key without tapping into lights wiring. Other than that, not too bad of an adventure.

p.s. I went 6.5" lights and had to bend my antenna towards the back at about 20 degree angle so it wasn't hitting the lamp.
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Old 06-24-2010, 12:56 AM   #8
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One of the cigarette lighters in the front switches on and off with the key. Use that to a relay coil, then a direct battery connection to the lights in series with the relay switch. Badabing badaboom now you have a nice source that has enough umph to power the lights. If you put a switch in the relay coil circuit, it can be a tiny one on the dash.
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Old 06-24-2010, 06:39 AM   #9
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Quote:
Originally Posted by Bionicrooster View Post
This is a dumb question but where do you tap in? I can see running the wires back to the switch (likely mounted in the dash) but then where do you take the wores to get power? Straight to the battery? To the fuse box?
Straight to the battery. Most light kits will come with a wiring harness that has complete instructions. The wiring is very simple and you don't have to "tap into" anything.
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Old 06-24-2010, 09:09 AM   #10
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daggo66 is probably right for the late models with computors. Just be sure to turn your lights off!
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Old 06-24-2010, 09:15 AM   #11
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I'm really sorry about all the trouble, I went thru this to, before I got the sPOD control system



It's a little expensive if you're just putting in a set of lights, but the 6-switch panel will take care of all lights/winch/ OBA/ Aux/-etc and it's ALL PRE WIRED AND RELAYED !!

I had done all my wiring/relay/light install previous, but when I had a problem, it was a PITA to trace--now no problemo

Checkitout --www.4x4s-pod.com

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Old 06-25-2010, 03:25 AM   #12
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That sPod set-up is nice!

Here is how the CAN bus was explained to me, as best I can relay (pun intended) to you: think of it as a power and info grid that runs like a railroad track all around the Jeep. Every electrical component joins or plugs into that grid to get power and to send/recieve data about its state or change in state, and any other devices that may relate to it functioning properly or as part of a subsystem. Anything beyond a device that is either on or off (such as a brake light bulb) probably has its own mini-computer/chip to assist in collating/processing all the data. So to continue the example, when you step on the brake pedal and the brake pedal switch/sensor trips, the ECU picks up the change in state on the bus and sends a signal via the bus to the brake light to turn on, and the master cylinder sees the same signal on the bus to give related/progressive brake pressure to the calipers according to how hard you push on the pedal. The feedback signal and wheel motion sensors are monitored by the anti-lock brake/anti-slip systems to see if either should engage and to what level, all monitored by the ECU to micro-adjust the engine for the most efficient engine/transmission output... it goes on and on and on, ever-changing and at milliseconds all the time. All the components "talk" to (and around) each other and to the ECU, thus the ECU back to those components individually or in systems to function as a whole, all via the bus. There are myriad simultaneous signals across the bus, not unlike how fiberoptic wires carry millions of phone calls, yet you (usually) only hear your conversation when another phone dials your number. This is why tapping into the bus to add new components, or modify existing ones can mess not just with that component but with the system. Take the incandescent brake bulbs for instance; the ECU is programmed to recognize a specific voltage, voltage change range, amp draw, time delay, etc. If you try to swap out for aftermarket LED bulbs, it is likely they won't work properly, or as advertised, if at all, as the ECU wont be seeing any or all of the expected parameters. Now imagine trying to do a "simple" HID headlight bulb upgrade (as I have wished). The bus was intended to simplify wiring, to reduce the amount of wire (and weight) used, and to simplify diagnostics (maybe for the trained OEM techs). In the grand scheme, it has become more complicated (in the sense that you now need computers to make most if not all trouble diagnosis) and expensive, but very reliable. It certainly has helped to insure the dealerships and the factory trained techs keep the lion's share of maintenance. Again, think of how you can connect multiple different gadgets to your PC with USB (really only limited by how many USB ports your PC has); each of those gadgets can see and talk to the other gadgets plugged in, and receive their power, all while the PC coordinates/orchestrates the whole enchilada for seamless functionality. Without some serious computer knowledge & training, you can't successfully hack into your PC, nor can you tap into a USB circuit to add another gadget into the mix, and you can't easily swap one gadget for an upgraded or different brand of the same gadget without changing some of the PC's software so it can correctly communicate with it. Who doesn't need or use their IMS people?

Well, that's basically how the Jeep does it, too.

That is far from a complete description, but I hope it helps some others get closer to understanding the CAN bus system. I'm still not sure I completely get it.
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Old 06-03-2011, 11:01 PM   #13
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Sorry to bump this thread, but this is the first one I've found in here on it, and searching Can bus system in here is useless since the words are too short for the search function.

Does the Can bus system come on the Chrysler 300's? Because my dad is trying to hook up a wiring harness for the trailer, and the brake lights won't work, he has the adapter to convert separate turns and brake lights to be one unit for the trailer wiring. But the brakes won't work, is this because it has a Can bus system that is seeing the extra power draw, so it deactivates the power to the brake lights?
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Old 06-04-2011, 02:16 AM   #14
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Originally Posted by deathphoenix99 View Post
Sorry to bump this thread, but this is the first one I've found in here on it, and searching Can bus system in here is useless since the words are too short for the search function.

Does the Can bus system come on the Chrysler 300's? Because my dad is trying to hook up a wiring harness for the trailer, and the brake lights won't work, he has the adapter to convert separate turns and brake lights to be one unit for the trailer wiring. But the brakes won't work, is this because it has a Can bus system that is seeing the extra power draw, so it deactivates the power to the brake lights?
This MAY be true. I don't know if the system monitors current draw but to do it is relatively easy. Where the system attaches the light to ground if you put a small resistance there, the computer could monitor over-current and disable the circuit in such situations. With that small resistor there it could also monitor the condition of the bulb filament to see if it is open by applying a small voltage to the light (not enough to light it up) and monitor to see if a voltage appears across the resistor. I wouldn't be surprised if they did that in this modern day of computers.

I got the factory installed tow package so I don't even know if they tapped the brake lights or not. Then I had a brake system installed for the hitch wiring and have no clue how they did it because a paid to have it installed by a camper place. All works well including the trailer lights and brakes. My trailer has a lot of pretty lights too! Makes her look all dressed up at night when the head lights are on.

That having been said, I have a CB and Ham radio and those are wired directly to the battery with my own fuse panel. If I wanted them to go on and off with the key, I would add a relay circuit to it and wire the relay coil to the cigarette lighter that goes on and off with the key.

I just purchased a winch. That...I am sure....will be wired directly to the battery. I haven't wired it yet but it sure does look purdy sittin' there on the bumper.
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Old 06-04-2011, 02:22 AM   #15
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So what exactly will happen if I use the Fog light power to trigger my relay for some aftermarket lights? The power for the lights is off of the battery, switch is just activated by the fog power.
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Old 06-04-2011, 02:33 AM   #16
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So what exactly will happen if I use the Fog light power to trigger my relay for some aftermarket lights? The power for the lights is off of the battery, switch is just activated by the fog power.
That works. Wire the relay coil to the lights right under the hood, no need to trace it back. The small current draw of the relay will have no effect on the system. Then wire the accessory lights directly from the battery through the relay contact NO (normally open) contact and vuallllla....your lights will work and no errors on the computer.
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Old 06-04-2011, 02:39 AM   #17
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Yeah, I've been running it that way for about 2-3 weeks. I tapped it right by the light socket.
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Old 06-04-2011, 02:55 AM   #18
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Yeah, I've been running it that way for about 2-3 weeks. I tapped it right by the light socket.
And no computer errors?
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Old 06-04-2011, 03:21 PM   #19
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Thanks guys

I came here to help me make a decision. The decision of whether to fix-up my YJ or to trade it in for a new JK. The JK sounds like a neat rig for a guy that doesn't mind budgeting "factory service" into the cost of ownership. If I was the guy that traded in his car every couple years and rarely if ever lifted the hood then I'd jump in with both feet. I thought it was over technofied and unethical to put a $30 voltage regulator inside the $750 PCM of my TJ but that was nothing compared to where we are now. Got to go warm up the YJ and blow the cobwebs out of the muffler.
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Old 06-04-2011, 06:00 PM   #20
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And no computer errors?
Nope.
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Old 06-05-2011, 08:01 AM   #21
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this is the easy and safe way to get power to your relay,, remember you only need a couple of milla volts to triger the relay.. all the power comes off the batt.. ATO/ATC Tapa Circuit™ Dual Fuse Holder - Wirthco Engineering, Inc.
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Old 06-05-2011, 08:13 AM   #22
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I wired my headlights & spots via the OE canbus; I retained the OE fogs. I went around the canbus for the floods.

If you want to use the OE circuits, you can't just t-tap to trigger a relay since the PWM cycles too low to hold it closed; I 'scoped the dang animal and posted the results in the "paging Hilldweller" thread.
To do it properly, use a capacitor inline and a diode on the back.

Worked great.

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Old 06-05-2011, 12:29 PM   #23
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Im not certain but I think the accessories are only warrented for one year from date of purchase.

Might want to check on that if its part of the decision on having the dealer do the install.

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