1985 yamaha 70 hp trouble with warning lights

1985 Yamaha outboard 70 HP. Bought motor used, had sat for 12 years, rebuilt carbs, replaced water pump kit.
Installed on new boat and test ran.
Do not have a green light on the engine gauge at any time.
have a red light and buzzer when running. Oil tank is half full. Engine heads are cool to touch. Runs like a scalded skunk, no limiting of RPM.
I believe it is a false alarm, but would like to prove it.

Troubleshooting the gauge shows only red light lights correctly, red light lights when green light should and yellow light does not light at all.
Apparently gauge is bad.

Can't find a source for the 3 light yamaha gauge, red light, yellow light and green light.


Why isn't it limiting RPM if it thinks there is a problem?

I believe the oil sensor only is for oil level on this engine? No way it could be sensing oil pump issues or old oil sludging in bottom of oil tank or in pump/lines? Marked level on oil tank and it appears to be using oil as I have test ran it.

Any way to disable oil level sensor or fasten it in up position?
Thanks for the help.
It is a beast of a little motor!

Re: 1985 yamaha 70 hp trouble with warning lights

Did that oil set up have the boat mounted oil tank that pumps oil to the motor mounted oil tank?
I think green light and the yellow worked off of the remote tank level switch.
Something to look into, as I have no real idea about the 70.

Yamaha only monitored level, no flow was monitored like Suzuki

Re: 1985 yamaha 70 hp trouble with warning lights

No, this 70 HP only has the engine mounted tank, fills through the cowling. Thinking I can replace the gauge with 3 LED lights, red, yellow and green,(essentially make a gauge) if I can figure out the right wiring to make all three work correctly. I'm going to test to see if I can ground out the various sensors and make them light 3 test lights correctly before buying the LEDs.

Re: 1985 yamaha 70 hp trouble with warning lights

Wrong guage. That engine doesn't use the three light system. It uses no lights, only an alarm for high temp or low oil level. Also there is no rpm limiting on that old of model

Re: 1985 yamaha 70 hp trouble with warning lights

The 3 lamp gauge matches factory wiring harness and what is in service manual.

Re: 1985 yamaha 70 hp trouble with warning lights

Yamaha uses the same harness for all engines. Just don't use all the wires.

Re: 1985 yamaha 70 hp trouble with warning lights

Yamaha must use the same service manual for all engines as well then. You just don't use all the pages.

I looked your business up on the internet. You should know a lot more about this than me! I'll quit with the satire.
The model specific service manual does show this gauge, however, and goes through the troubleshooting algorithm for it.

Re: 1985 yamaha 70 hp trouble with warning lights

The only oil sensor on your engine is a low oil sensor. It triggers the alarm and wired in with the high temp wiring. So if it alarms, you have to figure if its heat or oil yourself. There is no separate sensor to light the yellow or green light. The yellow is used with the main tank in the boat to tell you if that tank is getting low and it shuts down the oil transfer to the engine. Those lights need the three sensor module that goes in the tanks of the V4 and V6 engine. Are you looking at an orginal Yamaha manual or an aftermarket one?
As for your alarm, your float has sunk. It happens all the time on the older engines. You can replace the sensor in the bottom of the tank but the float is built in and not replaceable. Disconnect one of the blue wires coming out of the bottom of the tank and see if the alarm quits.
Been a Yamaha dealer since 1990 so I've seen one or two.

Re: 1985 yamaha 70 hp trouble with warning lights

Thanks, I will do just that when I get home next week.

Re: 1985 yamaha 70 hp trouble with warning lights

I have a green, green/red and a black ground wire from my oil level sensor. If I unplug the green wire from oil sensor, my alarm stays off.

According to manual, green wire grounds circuit when sensor says tank is half full, leaving green/red wire to ground circuit when tank totally empty. A two-level sensor, if you will. Does this sound right?
Will temp sensor circuit still work like this with green wire from oil sensor unplugged?