Another tachometer question

[maverick974]

1985 Johnson 150.
I've researched old threads on here and did the tests suggested and it looks like the regulator is good so I bought a new tach. Hooked it up and nothing. I even ran a new tach wire just to make sure there wasn't a problem with the tach wire.
Any suggestions?

 

[Joe Reeves]

Re: Another tachometer question

We have no idea just what tests you may have peformed. Did you do the following test? If not do so and let us know what you find.

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

 

[maverick974]

Re: Another tachometer question

Ok, I did the test but I'm not 100% sure I did it correctly. First of all, I bought a new tach so I'll assume at this point that the tach is in working order.
I installed the new tach. No worky. I then checked the positive and negative to make sure I at least had power to it. I then followed your advice and connected the grey wire to the yellow/grey wire on the terminal strip. Still no tach. So to check that there is no break in the grey tach wire, I hooked up a test wire from the yellow/grey wire to the tach and started the engine. Still no tach.
With that information, you would assume the rectifier is not working but it is. Last time on the lake, I brought my tester with me. Before I got in the water, I checked the battery. A little over 12 volts. After being on the lake all day, I checked the battery again. 13.2 volts so I am again assuming that the charging system is working.
I do have a question about if I tested the tach correctly. The yellow/grey wire is attached to the solid yellow wire. When testing, should I separate the yellow/grey wire from the solid yellow wire and if so, what do I do with the other wire?

 

[Joe Reeves]

Re: Another tachometer question

Your question of: "I do have a question about if I tested the tach correctly. The yellow/grey wire is attached to the solid yellow wire. When testing, should I separate the yellow/grey wire from the solid yellow wire and if so, what do I do with the other wire?" confuses me.

Normally, as per the wiring diagram below, the Yellow/Gray wire from the stator connects to the Yellow/Gray wire of the regulator/rectifier assembly, then Yellow to Yellow. However the later designed stators and regulator/rectifer assemblies did away with the Yellow/Gray wire code and went to all Yellow. If all Yellow on either the stator or the regulator/rectifier, it doesn't matter which Yellow wire connects to another Yellow or Yellow/Gray wire.

Note the Gray wire coming into the terminal strip at an angle. That's the gray lead that leads to the tachometer sensor terminal, and this is the one that would be disconnected and then connected to one of the stator Yellow or Yellow/Gray leads as per the test I provided.

The dial on the back of your tachometer.... is it set to number 6 as it should be? The tachometer needle may be resting at some various point on the dial when the key is OFF, but as soon as you turn the key on, that needle should drop to zero instantly... does it?

 

[maverick974]

Re: Another tachometer question

Your question of: "I do have a question about if I tested the tach correctly. The yellow/grey wire is attached to the solid yellow wire. When testing, should I separate the yellow/grey wire from the solid yellow wire and if so, what do I do with the other wire?" confuses me.

Normally, as per the wiring diagram below, the Yellow/Gray wire from the stator connects to the Yellow/Gray wire of the regulator/rectifier assembly, then Yellow to Yellow. However the later designed stators and regulator/rectifer assemblies did away with the Yellow/Gray wire code and went to all Yellow. If all Yellow on either the stator or the regulator/rectifier, it doesn't matter which Yellow wire connects to another Yellow or Yellow/Gray wire.

Note the Gray wire coming into the terminal strip at an angle. That's the gray lead that leads to the tachometer sensor terminal, and this is the one that would be disconnected and then connected to one of the stator Yellow or Yellow/Gray leads as per the test I provided.

The dial on the back of your tachometer.... is it set to number 6 as it should be? The tachometer needle may be resting at some various point on the dial when the key is OFF, but as soon as you turn the key on, that needle should drop to zero instantly... does it?

Yes, the tach is on 6 and the needle sits on 0 as it should. When I turn the key on, the needle jumps just a smidge and then goes back to zero.

 

[Joe Reeves]

Re: Another tachometer question

If your charging system is indeed functioning, and the tachometer is new, the tachometer should be working if the wiring is correct.

The test I entered above..... the only wire that is to be disconnected is the "Gray" wire that leads to the tachometer so that it can be connected to one of the Yellow leads that flows from the stator. No other wire is to be disconnected.

The tachometer ground must be a true battery negative ground... that is a connection that leads directly to the negative portion of the battery, NOT connected to some black ground wire that is leading from some accessory such as a radio, depth sounder, etc. Voltage being applied to a radio etc has voltage flowing thru it of course but it also has voltage flowing back thru its ground wire which may conflict with another component (tach) if it is wired into it.