200 Merc Tach has AC voltage on send, but does not move

[ajhabbit]

Hello, I recently bought an Amega tachometer and would like to know if there is a simple procedure I can perform to test the tachometer. When the power is turned on, the tachometer needle moves to zero, but when I start the engine, the needle does not move off of zero. I had an older Teleflex tachometer on the boat and the needle would slowly wonder about thousand RPM higher than normal. I would tap the gauge and it would seem to go back to the correct RPM. When the old gauge went out completely, I got the new gauge and all of the connections on the tachometer were the same so I moved one wire at a time. I feel confident that the wires are connected to the gauge correctly. Using a multi-meter, I tested the ignition pole on the back of the tach and it reads 12.5 volts when the engine is off and 16 volts while idling. When I set the multi-meter to 200 vac, I get 17 to 20 on the send wire at the back of the tachometer while the engine is idling. The documentation which came with the tachometer said that I should have between 5 and 7 volts AC on the send at the back of the tachometer. My tachometer’s send pole is connected to the grey wire coming from the rectifier. Could this mean the rectifier is sending too much voltage or the tachometer is bad or do I need to perform other test?<br /><br />The tachometer is installed on a 1996 200hp Mercury EFI motor. The tachometer is set to 6P.<br /><br />Thanks In Advance <br />Alex

 

[Hooty]

Re: 200 Merc Tach has AC voltage on send, but does not move

The 5-7 vac at approx. 2000rpm should be measured between ground and the gray wire which must be connected to the "S"post on the back of the instrument. The gray wire should connect to a yellow wire at the rectifier. It's reading ac voltage from the alternator, not dc voltage from the rectifier. <br />These are Teleflex instructions but they''re just like yours.<br /><br /> Teleflex <br /><br />c/6<br />Hooty

 

[ajhabbit]

Re: 200 Merc Tach has AC voltage on send, but does not move

The grey wire is coming out of the rectifier. I have yellow wires which go to the Stator and red wires that go to the solenoid next to the power packs. I do not know how to test the stator, but I assume the engine must be running while testing. The yellow and red wires seem to have 12VDC while the engine is off and the grey wire has 17-20VAC while running. A Teleflex support representative sent me an email today saying the signal voltage may stay too high for the tachometer to detect the start of a positive pulse. I did read in another post that it is possible to get 17VAC at the back of the tach. I guess the problem is that I do not know what is normal for my motor. It is looking like 17-20 VAC is too high.

 

[Hooty]

Re: 200 Merc Tach has AC voltage on send, but does not move

I'm suspicious of the rectifier now. Have you had a problem with the battery not charging?<br /><br />c/6<br />Hooty

 

[ajhabbit]

Re: 200 Merc Tach has AC voltage on send, but does not move

I did buy a new battery recently, but that was because the oil reservoir was holding the battery in place and when I took it out the battery fell over and all of the fluid leaked out. Beside that the battery has been charging fine. I have been wondering if the motor has been overcharging my battery. When the motor is off my voltage gauge reads 12.5 on the dashboard, but when the engine is idling it reads 15.5. When I idle it up a little, the volt gauge goes up to 17 volts. It never went over 17 volts, but kind of made me wonder because I think 17 volts is sort of pushing it. Actually I don't know, maybe 17 is too high. I had read something about testing the resistance of the rectifier. If I understood it correctly this is done with the engine off. I believe it said to use an OHM meter and put the red lead on the yellow wire and the black lead from the OHM meter to the red wire. It then said to switch the wires around. This is the part that I was not sure about. It said that one way I should get resistance "I Think" or maybe not get resistance and when the wires are switched it will show no resistance. It said one way will show continuity and the other shouldn't. Not exactly sure what continuity looks like on my multi-meter.