Testing the Gray wire on my control box for a Tachometer

my 1986 90 hp evinrude did not come with a tach. I wanted to know if I have a siginal before I purchase one.

1. My battery is charging
2. My test light goes off when I test the gray lead from the control box.

Is there anything to test to see if I have signal off the powerhead?

What tools will I need?

I would love to get my tach to work

Thank you

Re: Testing the Gray wire on my control box for a Tachometer

The tachometer must be one that operates off of the charging system. Since your battery charges via the engine, obviously your engine qualifies..... standard on the 1986 90hp Evinrude/Johnson engine.

The charging system of that engine emits six (6) pulses.

Purchase a tachometer that has a dial on the back which can be set to number six (6).

Re: Testing the Gray wire on my control box for a Tachometer

Thanks Joe

Im shopping now for a new tach

Joe Reeves said:

The tachometer must be one that operates off of the charging system. Since your battery charges via the engine, obviously your engine qualifies..... standard on the 1986 90hp Evinrude/Johnson engine.

The charging system of that engine emits six (6) pulses.

Purchase a tachometer that has a dial on the back which can be set to number six (6).

Click to expand...

Re: Testing the Gray wire on my control box for a Tachometer

They are readily available here on iboats. You will need to connect a 2,000 ohm resistor between the signal and ground terminals of the tach if your engine has an unregulated charging system. The unregulated ones have the rectifier on the side of the engine, regulated are on top, under the flywheel.

Re: Testing the Gray wire on my control box for a Tachometer

kjdunne said:

You will need to connect a 2,000 ohm resistor between the signal and ground terminals of the tach if your engine has an unregulated charging system.

Click to expand...

I'm not aware of that requirement, have never installed the resistor, and have never encountered a problem with any tachometer. What is the purpose of the resistor? I assume there was a bulletin issued... where might I find it?

Re: Testing the Gray wire on my control box for a Tachometer

Referred to ground you have only a definite signal on the gray lead (rectifier-only system) when two of the rectifier's diodes are conducting. At low rpm the stator produces low voltage and there are certain periods of time around the zero crosses when the stator produces a voltage less than battery voltage plus 1.4V. In this time none of the recifier's diodes is conducting. In this time the gray wire is floating referred to ground and the voltage can be any anywhere between -0.7V and battery voltage + 0.7V. So voltage glitches and double pulses are possible. The resistor pulls the voltage down to zero in the floating times.
Many tachs include a resistor to ground, but obviously not all.
BTW the VRO also includes 1,000 ohms to ground for the same reason. So if there is a VRO and the gray and black wires are still connected there is no need to add one more resistor.

Re: Testing the Gray wire on my control box for a Tachometer

Interesting. I've been in this line of work in a serious manner since 1960, retiring in 1991 due to a injury. Strange that I've never ran across that information and will make a note of it.

Fishyfishy18..... Your 1986 90hp could have either type rectifier.

If you have a rectangular device bolted to the top of your powerhead, just in back of the flywheel, that has two yellow wires, a gray wire, a red wire attached to it, that would be a water cooled regulator/rectifier and your charging system would be regulated.

If you have a smaller round dome type rectifier with a triangular base that has but two yellow wires and one red wire attached to it, your charging system is not regulated. This rectifier is simply air cooled and usually ataches to the starboard side of the powerhead with two different size bolts.

Re: Testing the Gray wire on my control box for a Tachometer

I'm with Joe on this, however I do remember years ago that Teleflex tachs had problems reading the OMC signals from the integrated regulators that genereated a square wave tach pulse, so a resistor was added to help the Teleflex gauge until they were re-engineered.

Re: Testing the Gray wire on my control box for a Tachometer

fishyfishy18,do you have the original control box?right below the key is a plug receptical,you buy a harness for omc and tac and away you go!my 82 90hp had it i cant see why your 86 wouldnt.also with joe and others,you do not need any extra goodies .if you go to brp you will seee that all 90,s for many years had a round rectifer assembly and all had remote boxes with the plug just below the key.i never added any extra resisters to my motor and had zero issues for the life of the motor (10 plus years for me).see part 22.also see part 50 which only deals with motors with t/t.i wonder if thats where people are getting confused a little?