Yamaha Tach Jumpy

[chummy70]

Anyone have yamaha tach problem tach sometimes only reads half rpms then will show correct rpms then go to half. It's on 1988 yamaha 70 hp etlg with trim and the 3 oil warnings on it green yellow red. Checked all wiring but were does tach get readings from the 3 cylinders ? Thanks

[boscoe99]

Anyone have yamaha tach problem many have tachometer problems due to various reasons tach sometimes only reads half rpms then will show correct rpms then go to half. It's on 1988 yamaha 70 hp etlg with trim and the 3 oil warnings on it green yellow red. Checked all wiring but were does tach get readings from the 3 cylinders ? Thanks

There is a coil (one of four) under the flywheel that is known as the lighting coil. That coil will have two wires coming from it. Both are green. One green wire goes directly to the rectifier. The other green wire goes to both the rectifier and the main engine harness ten pin electrical harness connector at the front of the motor. There will be a connection point where the green wire from the lighting coil branches off to two other green wires, one to the rectifier and one to the ten pin connector.

The ten pin connector at the front of the motor connects to another ten pin connector in the electrical harness that runs from the motor to the key switch. Somewhere at the key switch a single green wire runs to the single green wire at the back of the tachometer. Any and all electrical connections should be inspected, from the lighting coil to the tachometer. The mere act of disconnecting and then reconnecting them (maybe several times) will sometimes solve an electrical connectivity problem.

Have you independently inspected the tachometer? If I mention a "wall wart" (120 volts AC to 12 volts DC transformer) would you know what I am talking about? If you have an old one laying around, it can be used to test the tachometer. What is your skill/confidence level doing electrical work?