cb related issue(i think), need help.

[Mhannink]

ok first off the truck is an 08 ford 450. i know its not a dodge but i think for this problem it may not matter too much.



last week i installed a cobra 18 cb radio and 4ft firestick antenna on my friends truck. the cb is wired straight to the battery and not through any of the factory electrical. it is also grounded straight to the battery. the install went smoothly, and the radio seems to work just fine.



the problem. a few days ago my friend calls me and says the lights on the truck are turning on and off randomly. after a little work discussion it seems, to me, that the lights are kicking on and off as if triggered by the keyless entry system, it also seems to be happening about the time her parents each left for work. the other thing i recall, when i was showing her how to use the radio, was i heard a car horn through the radio. it was someone hitting their lock button near by, the car horn honks and locks the doors. the cb and the truck were off at the time, but the radio honked.



im thinking that the radio is picking up the key fob signals and telling the computer to do the assigned tasks. is this really possible? there is a lot about radio's that are still black majic to me. whats going on here, and how do i fix it?



something i should note, the radio has 3 wires coming out of it. one is supposed to be hooked into a keyed 12v+ wire, one is a constant 12v+, and the last is ground. i hooked the two positive wires together, straight to the battery, im scared to touch the wiring on this truck as it is a little crazy, my biggest fear is that she will be stuck on the side of the road with horses on, i dont need to be worried about whether what i have done to the truck is stranding her or not. will connecting the wires corectly make a difference? what are my options for getting rid of this interference.

 

[Alan Reagan]

The first thing I would do is isolate the problem. Disconnect the radio from the battery and see if the problem goes away. If it does, then you probably have a wiring issue.



How did you run the wires from the battery to the radio? Accross the fender or down by the ECM. Usually you would just get some interference on the radio. One thing you might try if you think the 12V supply is picking up "signals" is to go to Radio Shack and pick up a noise filter for the DC line.

The 12V supply could be acting like an antenna for spurious signals.



Finally, you might want to ground your antenna to the frame (depending on how you mounted it. I mean, ensure the mounting base is mounted. I know the coax grounds the antenna back to the battery. I had a CB in my 01 and was picking up the electric fuel pump static till I grounded the antenna base.

 

[Mhannink]

ill try those things when i get a chance. she called me this morning and said her truck was dead. i dont know if its the cb issue or that it sat for a few days and has not been started. so it could be a battery issue. i do want to check those too i think. can anyone refresh me on how to do a parasitic draw test. ive done them before but its been so long i cant remember the details.

 

[Hitec.Redneck]

Where is the antenna mounted? It sounds like you have a grounding problem and or the antenna is located near some electronics and the RF from the radio is causing the horn, lights and other things to come on. I am a HAM radio operator and have had many of the same issue you have described. In one vehicle the antenna mounting location caused the windshield wipers to activate.



The frequency that the remote fobs use are much higher in frequency, cb radio is in the 27 Mhz most fobs are much higher in frequency and they should not interfere with each other.



If the antenna is not properly tuned so the SWR is low will cause stray RF to affect other circuits. Also the quality of the coax makes a huge difference, not all coax has good shielding so when transmitting the coax will actually radiate and not the antenna.



Make sure where ever the antenna is mounted that it has a good ground the the frame of the vehicle. Many vehicles do not have a good ground from a fender, headache rack, toolbox directly to the frame. I have a friend that runs 1500 watts on HF in his car and we had to install ground straps from all the body panels to the frame to stop all kinds of bizarre things from happening from transmitting that much power.