Tach acting up

[Grant Brown]

87 70hp 3cyl Mercury - My tachometer jumps around all over the place and rarely shows a reading that's even near to what the engine is doing. When the engine/ignition is off, it stays at about 1100 rpm. It's done this ever since I've owned the boat (3 years) and now I'm finally getting a chance to look at it.
What p/n should I look for to replace it?

Thanks

 

[ricksrster]

Re: Tach acting up

It will stay at a strange number when you turn it off. It should return to zero when you turn your key on.
Check all your wiring connections at tach tach and ground. Check your connection at rectifier rectfier. It should attached attched to the same post as either of the yellow wires.

 

[ricksrster]

Re: Tach acting up

Here is a troubleshooting guide.
http://ww2.tflx.com/pdf/obtach~1.pdf