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Old 02-23-2014, 10:09 PM   #1
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CB/aftermarket radio not playing nice

One of the first mods to my 13 jk was a cobra cb. It's the baseline 40$ model. Installed under the driver's seat. For power I tapped into the ignition controlled 12v cigarette port in the dash. No problems. Then I installed a kenwood dpx500bt head unit with the pac can harness and the pac harness for steering wheel controls. Recently noticed when out wheeling if I transmit on my cb the radio, dash gauges lose power, I get a chime, and the windshield wipers go across once. The cb still has power during this because I can still transmit. Also threw a code, not positive it's due to this but pretty sure, it's the lost communication with radio code.

Now this doesn't happen every time I key up but it did happens few times so I stopped using my cb in fear I fry something.

Maybe a bad ground? Or loose contact? Or maybe too much power being pulled from the power source?

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Old 02-24-2014, 09:39 AM   #2
Knows a couple things...

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Basic CB Radio Installation 101 is that CBs need to get their power directly from the battery. Probably the very worst source of power is from the cigarette lighter wiring which can cause problems just like you're having.

2-way radios including ham and CB can cause problems or pick up all kinds of noise from things like the alternator, ignition, etc. if you get the power from anywhere but directly from the battery. I don't know the JK but if the JK has a PDC (Power Distribution Center) in the engine compartment that is full of relays & fuses, the odds are good that it has a single heavy power wire feeding it directly from the battery. That wire would be attached to a heavy lug with a nut on top, you could connect your CB's power wire there to avoid connecting onto the battery connector.

Don't worry about the CB not turning off with the ignition by wiring it like that. CB radios don't draw even close to enough power to drain the battery when accidentally left on unless you left it on for weeks without starting the engine. Plus there will be times you want to use your CB offroad without the ignition being on.

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Old 02-24-2014, 12:30 PM   #3
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Wanted to help you out, but Jerry did it for me. He's spot on in his reply.
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Old 02-25-2014, 09:30 PM   #4
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Quote:
Originally Posted by Jerry Bransford View Post
... the odds are good that it has a single heavy power wire feeding it directly from the battery. That wire would be attached to a heavy lug with a nut on top, you could connect your CB's power wire there to avoid connecting onto the battery connector...
It should not have to be said, but for safety's sake, we need to say it anyway...
Yes, power the CB from the battery.
But make sure you have a fuse inline on the positive side.

You'd think that this would be a no-brainer.
But people have a way about taking shortcuts when it comes to wiring their automotive electronics.
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Old 03-03-2014, 01:39 AM   #5
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Thanks guys for the help, will deffinately re wire it to the battery. And yes I am running an inline fuse, but thank you for pointing that out!
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Old 03-03-2014, 11:08 AM   #6
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It should not have to be said, but for safety's sake, we need to say it anyway...
Yes, power the CB from the battery.
But make sure you have a fuse inline on the positive side.

You'd think that this would be a no-brainer.
But people have a way about taking shortcuts when it comes to wiring their automotive electronics.
And the fuse should be very close to the battery connection. Definitely before the wire passes through any sheetmetal.
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Old 05-19-2014, 07:09 PM   #7
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CB follow up

Question for the OP. Did changing the power source for your CB make the dash light/ windshield wiper gremlins go away? Did you find any other solutions? I'm having the same problem and it's making me crazy.
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Old 05-20-2014, 11:50 AM   #8
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In addition to power direct from the battery, GOOD grounding, both near the CB and at the antenna is a must.

Stray RF (transmit) energy getting into the vehicles electrical system can cause the OP's problem and worse can fry electronics in the PDU / ECM.

Short ground cables with good metal to metal contact between the radio to the chassis and the antenna to the chassis will do the trick.
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Old 06-24-2014, 11:05 AM   #9
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So, I've now run into this issue. I installed the CB before last wheeling season and it worked fine all year. As part of my winter upgrades, I had a new Kenwood head unit installed. Went out on the trails for the 1st time this weekend and have the radio reset, dash lights come on and wipers activate when I key the mic. I can transmit and receive with the CB fine when this happens. My power for the CB comes directly off the battery and the ground is behind the little panel on the passenger side right where the positive pokes through the foam into the engine bay.
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Old 06-24-2014, 03:13 PM   #10
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So, I've now run into this issue. I installed the CB before last wheeling season and it worked fine all year. As part of my winter upgrades, I had a new Kenwood head unit installed. Went out on the trails for the 1st time this weekend and have the radio reset, dash lights come on and wipers activate when I key the mic. I can transmit and receive with the CB fine when this happens. My power for the CB comes directly off the battery and the ground is behind the little panel on the passenger side right where the positive pokes through the foam into the engine bay.

Posts # 8 & #9 bring the subject of grounding in a high RF environment into focus. The subject of "Proper Grounding" almost always misses the point that there is NO RF free point in a vehicle with an operating transmitter.

The common observation that high VSWR "causes" electrical system malfunctions is certainly valid. It is because the return power from the antenna energizes the chassis with RF energy. In addition to the rather high RF field radiated by the chassis, RF currents flow thru the common grounds of all the electronics in the vehicle. These currents are not predictable in their amplitudes or locations, but the higher currents cause higher localized RF radiation. The process can be difficult to visualize and test equipment to aid troubleshooting is not commonly available to the hobbyist. Even when VSWR readings are low, the problem remains, although usually at sufficiently reduced levels to remain invisible......unless something in the distributed ground system is changed...such as a new addition of a head unit, that may not have the same "immunity" to common mode RF as its predecessor. A ground relocated by just a few inches can make a large change in interference. Most hard mounted equipment can't take advantage of this technique.

We must remember that our "Ground" is actually a functioning element of the antenna. The chances of electrical malfunctions is reduced by selecting the ground points that have the least RF current associate with them. If reducing the VSWR to absolute minimum is not sufficient, then cut and try with relocating other component grounds may work.


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Old 07-24-2014, 12:33 AM   #11
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After grounding the antenna and the CB ( separate ground wires to the chassis) and taking pos/neg power from the battery, with no change in the wiper and dash lights issues, I unplugged the harness between the PAC interface and the original radio harness. Presto, the gremlins went away. Plugged the harness back together and the wipers wiped and the dash lights lit one time even though the CB wasn't even connected. So is it the head unit or the PAC interface? More investigation is necessary.
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Old 07-28-2014, 03:14 PM   #12
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So I just went back to the audio shop with all of this info, and got to talk with an installer who has seen this specific problem in the JK's. He confirmed it was the PAC that causes it and recommended we try a different type of module. He installed this in place of the PAC and problem solved. While having a good ground will solve many problems, this wasn't one. I had good grounds and was able to get a good tune on my CB. It is the aftermarket PAC that causes this particular problem.
Hope this helps you out!
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Old 07-31-2014, 11:17 PM   #13
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Thanks chuckr, that's great news about the PAC module. The link isn't clear which module you installed. Would you tell me the part number? I'm ready to try anything!
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Old 08-02-2014, 05:50 PM   #14
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... He confirmed it was the PAC that causes it and recommended we try a different type of module ... It is the aftermarket PAC that causes this particular problem...
What is a "PAC"?
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Old 08-03-2014, 02:01 AM   #15
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A PAC is a brand of an interface that goes between an aftermarket radio and the totally complicated computer bus in a JK or JKU. In mine it allows the aftermarket back-up camera to know when the Jeep is in reverse. It was all installed by the first owner who didn't run a CB. When I installed the CB, all these gremlins showed up.

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