I Have A 04 90 Yamaha I Was Fishing The Other Day And Smelled Smoke. Went Back And The Tach Was Smoking The Face Was Glowing Red. Disconnected I Have A New Tach I. Was Just Wondering If Anything Else Could Cause This Problem Before I Install The New One?

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LET UM GO TO GROW

No expert, but before I installed the new one, I'd check all the connections (guages are usually jumped from one to another for power and ground) and make dang sure the power is fused with the proper size fuse. From what you describe, that tach could have caught the boat on fire.

Wannabe...

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A kinder, gentler Wannabe, but still prettier than you.

Several things to check before you install the new one. Your tach requires 3 connections to work. 4 if you want the background light to work. Check the ground wire to be sure you have a good solid ground. Next is the power wire (12V). This normally comes from the purple wire on your ignition switch. Most important is the send wire, normally gray. The gray wire is connected to one of the yellow wires coming from the stator. This connection is made at the rectifier/regulator because these wires also feed the rectifier. The rectifier is the most common souce of tach and or charging problems. They are very sensitive and creating a spark or hooking a battery up backwards, even for a split second will blow them. With all that said, check your charging circuit. The simplest way is to check your battery voltage with the motor off. Then check it again with the motor running. If working properly you will see an increase in voltage. This can be done with a meter at the battery. Or if your depth finder is connected to the starting battery, a lot of them have the capability of monitoring battery voltage.

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Fair Winds and Following Seas

Bill H. PTC USN Ret
Chesapeake, Va

Thumbs up on the rectifier...fixing to change mine.

If anyone has trouble with a rectifier on an older merc let me know. I have an easy cheap and better alternative for those. Actually you could probably use it on any system that was less than 20amps. Radio Shack makes what is called a "full wave" rectfier and does a better job of regulating than the old ones did. That and they are like 3 bucks apiece...lol. I had two spares when I was running an old merc 1150. Worked like a charm...was smaller...controlled voltage better...and didnt' cost 50 bucks.

My new one on the johnnyrude is water cooled and about 150....

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Doc Holiday; "I'm your Huckleberry" "You ain't no Daisy"

Hey IBNFSHN...While you are on the subject of tach's and rectifers I also need some help. I have a 1994 Basstracker with a 60 hp. merc and the voltage meter does not go up past the middle and most of the time is showing discharge. Also my Tach has quit working. When I put a voltage meter on the battery it registers 12.5 volts and then I start the motor and it will ever so slowly go up to about 13.5. What do I need to do first? I know very little about Boat motors...

You need to test your rectifier. Here's how you do it.

Testing Merc’s square rectifier
If you use an analog meter set it on the RX1000 scale.
If using a digital meter, set it on the diode symbol.
1. Disconnect the battery leads.
2. Disconnect all wires on the rectifier.
3. Connect the red test lead to ground and the black lead alternately to terminals A and C.
The meter should show continuity.
4. Connect the black lead to gound and the red lead alternately to terminals A and C.
The meter should not show continuity.
5. Connect the black lead to terminal B and the red lead alternately to terminals A and C.
The meter should show continuity.
6. Connect the red lead to terminal B and the black lead alternately to terminals A and C.
The meter should not show continuity.
7. Replace the rectifier if you do not get correct readings.

Attached Images

 

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Fair Winds and Following Seas

Bill H. PTC USN Ret
Chesapeake, Va

Thanks...IBNFSHN.....I will give that a try.....

IBNFSHN....You were right...I replaced my voltage regulator (on my boat that is what they called it) and it fixed my voltage problem and my tach...Mine ended up looking different from your picture but I found it and replaced it. It did the trick. Thanks so much for your help....

IBNFSHN I have a 94 120 johnson that the tach dosen't work right. It bounces all diffrent ranges but some times it works properly till I change speed then it starts bouncing all over the place from no reading to correct reading. Any suggestions?

Good news. Your rectifier is a part of the regulator.

__________________
Fair Winds and Following Seas

Bill H. PTC USN Ret
Chesapeake, Va