Tacho problem with a 60 HP 3 cyl. 2 stroke year 1996 engine

[Ole1972]

Hi guys

I get No Reading on my tacho when i am out sailling.
What can cause that problem.
I have power on ign when the key is switched and light in the
tacho.
Gray cord is at send
Purple cord at Ign
Balck cord at grd.

 

[haventaclue]

Check your rectifier/regulator would be my first thought