Aside from putting 13.8 to the yellow wire you also have to provide the same 13.8 volts to the red wire.
Have you taken the front faceplate off and (gently) checked the ribbon cable that connects the faceplate to the radio body? The reason I ask is that one of the TK-8180 radios I purchased was listed as non working. Which it was until I checked the ribbon cable and found it wasn't inserted fully into the body. I surmised that someone previously had the KRK-10 remote kit in use and when converting the radio back, they did not fully insert the ribbon cable back in.
Just a thought. Good luck!!