That is the WRONG power cord for the C-29, but will work, don't connect the middle yellow wire to anything. Tape it, or just cut it off, you don't need it.
That power cord is for some older "Plus" models that required constant power to the CPU/PLL in order for it to retain what channel you were on when you turn off the radio. If you didn't hook up the yellow wire, the radio would always go to channel 9 when powered up. Think of the yellow wire as the same as your car stereo. Even with the car off, in order for it to retain your car stereo's programmed stations in memory, it needs constant power - which is the yellow wire. The Yellow wire is ment to be hooked directly to the car's battery.
The Cobra 18 from a few years ago and going back into the 90's, also needed a constant power source to retain what channel you were on when you power it back on. It's cheaper for them to add the yellow wire than make a PLL that is capable of retaining the last channel. The newer Cobra 18's have a newer pll capable of retaining last channel, so they "thankfully" removed the yellow wire that confusses many.
The cobra 29 has a manual encoded channel selector to the PLL, so constant power is never needed to retain last channel information - its manual!
