97 120 Tachometer is acting weird

[stssa]

Last sunday when I took the boat out, I noticed my tach was going all over the place. on full throttle it was going beyond 6K and all of a sudden it stopped working and after a while it came back on but It was not a smooth needle movement, I would give a little throttle and needle would jump 3k 4K. These engines get that ignition signal from stator charging pulse. Since my voltmeter was showing right amount of charge I assume its not the stator. Im thinking either my Regulator or the gauge is going south. Has anyone had this problem and what was the faulty part?

 

[TwoFish]

Re: 97 120 Tachometer is acting weird

Had the same problem and fixed it a couple of weeks ago. I have a 1998 - 75hp so would think your motor has a similar setup. I?m only new to working on outboards so I?m no expert.

It as only a corroded connection on the grey signal wire from the regulator. Mine was in the main wiring connector at the back of the motor. Used the ohms setting on a multi meter and found some resistance in the wire. Traced it back to the connector. Cleaned it up and the tacho now works.

The regulator on mine has 4 wires. I?ll look up the colors when I?m near the manual. From left to right from memory.

Two yellow that come from the stator( ac current).

One grey signal wire to the tacho. This is essentially only one of the stator wires that has a filter on it. If the filter is broken it is still possible for the regulator to charge correctly but not send a good signal to the tacho. I haven?t tried it but I understand it is possible to get a signal to the tacho from one of the stator wires.

One red wire. Positive wire to the engine (DC current)

The regulator on mine grounds itself to the engine through the body of the regulator. Some regulators have a black ground wire. Check to see if the regulator has a good ground.

I was planning to run a new wire from the grey wire on the regulator to the back of the tacho if I could not find a bad connection. This would be another way to help diagnose the problem.

Good Luck

 

[stssa]

Re: 97 120 Tachometer is acting weird

Thanks for the advise I will definately check mine tonight. Did you have corrosion inside the connector?

 

[TwoFish]

Re: 97 120 Tachometer is acting weird

Hi stssa,

Yes the corrosion was inside the multi-pin main loom connector, on the back of the motor. The corrosion was on the pin side of the connector at the base of the pin causing two of the pins short out. This was sending electrical interference to the tacho causing it to read high from time to time. Once I cleaned the corrosion off, it worked fine. Luckilly the corrosion was on the outside face of the plug & not inside the wiring loom behind the plug. I would have needed to run a new wire from the regulator to the tacho in that case.

You will be able to look at you service manual to work out which pin is which.
Look along the wires to see if the insulation has any cracks or splits.

On my motor there are 5 connections between the regulator & the tacho.

Working from the regulator.

1. A bullet connector connecting the grey wire from the regulator to the main loom.

2. The large multi pin connector at the back of the motor. Connecting the engine loom to the boat?s loom.

3. Another multi pin connector near the forward controls. Connecting the boat?s loom to the controls.

4. A smaller multi pin connector coming from the forward control to the gauges.

5. The connection on the back of the tacho.


I cant remember where I read an article on troubleshooting boat tachos but it said if the tacho is reading high it will be the result of electrical interference on the signal wire. If the reading is low, the signal is weak (corrosion or frayed wire). If the tacho cuts in and out (especially if the light flickers on & off) it would be one of the power wires to the tacho. This supposes the tacho & regulator are working properly.


I would think the quickest way of finding out if your problem is a short in the signal wire, is to run a temporary wire from the grey wire on the regulator to the back of the tacho & see if this fixes the problem.

Hope it only a wiring problem.

 

[stssa]

Re: 97 120 Tachometer is acting weird

I will disconnect the main connector in the back and see signs of any corrosion. If there isnt any I will run a wire and make sure thats the problem before I start taking the control box off. Thanks for the advise I really appreciate it.