If it came with the motor it shouls be a resistor plug. They usually will have an "r" somewhere in the designation(such as NGK plug cmr7h) to designate resistor. Also look for metal to metal contact that can create interference. Do you get interference only when the engine is running? If you have problems with interference without the engine running there is some other problem. Radio glitches can be very hard to track down. If the problems are only when the boat is in the water running Spektrum brand radios are known to have some problems with water and the company themselves suggest you not use most of their radios in boats. Doug