Red plug harness gives you the option to use new control boxes with key push choke, fast idle lever, kill lanyard, etc.

HOWEVER, it’s hit or miss if the single lever box will let you get full F-N-R shifting.

The metal shift lever style motors need a long sweep to get into gear. The "newer" plastic shift lever motors dont need as much sweep at the control box and work with the white/black control boxes. Beware of this compatibility issue!