Speedometers are independent of the outboard. But some have the pickups built into the gearcase. Otherwise a pitot tube attaches to the back of the boat. It's realy a pressure gauge. Water forced into a tiny hole pressurizes the air in the speedometer hose and that's what moves the needle, but instead of PSI, it's graduated in MPH.
Tachometers are adaptable to most any kind of outboard. You'll need a harness that plugs into the throttle/shift control, available at Johnson/Evinrude dealers. The wires you need to use are as follows...
Purple is Key-on and goes to the I or Ign post
Black is ground and goes to the G or Gnd post
Gray is the signal and attaches to the S or Snd post
They the light is either powered by the I whenever the key is on, or from a separate blue wire used for the navigation lights.
