MercuryTach question

[finish line 88]

2003 Mercury 115 - 4 cylinder 2 stroke. Batteries were not charging so I replaced the rectifier. I'm getting 14.7 volts now at the batteries. Tach worked fine but the next day I have no tach. Checked the pulse at the tach and have 12.5 volts. Is there anyway to test tach ? Any help with this would be great. Thanks

 

[wrench 3]

Assuming that you have an analog tach. If you put an old fashion incandescent test light on the signal wire to the tach it should flash on and off (more like a flicker) with the engine idling. If it's steady you have a problem with the signal. If you have 12V, ground and a flashing signal, a good tach should be doing something.

 

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Yes it is a analog tach. I am testing on the gray wire. There is no difference in the test light if the motor is running or not. It is a stead bright light. I guess the new rectifier is faulty. Thanks for the help.

 

[sutor623]

Lots of times the rectifier will fail if there is an issue with the stator. Go to the link in my sig to CDI electronics and troubleshoot your stator before throwing another rectifier at it.

 

[wrench 3]

Is there any possibility that you got the wiring mixed up on the regulator?

 

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I came down the rectifier and did one wire at a time. Black to ground,red to red, yellow to yellow, and gray to gray. Does it matter which red to red and yellow to yellow ? One thing I notice is the tach sits at around 400 rpm with the key off. When key is on it goes to zero.

 

[sutor623]

Yes it does matter which way the meter is set, at least on the red leads. The red leads should have a one way diode in it that will only read one direction. If it reads both ways, the regulator is blown. If you blew the diode you either

A.) hooked the battery up wrong, even for an instant!!
B.) have an issue upstream (likely the stator coils)
C.) have a short in your wiring harness somewhere.

 

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I was asking if it mattered which red and yellow leads from the engine plugged into the red and yellow leads on the rectifier ? Turned the batteries off at the battery switch so they were not hooked up wrong. Have 14.7 volts at the batteries while engine is running so it's charging.

 

[wrench 3]

It doesn't mater. The two reds are interchangeable, as are the two yellows.

 

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I switched the gray wire to the yellow and the tach works. I ordered a new rectifier. Thanks for the help.

 

[GA_Boater]

I switched the gray wire to the yellow and the tach works. I ordered a new rectifier. Thanks for the help.

Save your money. Getting 14.7 at the battery shows a good rectifier.

The tach wire was on the 12 volt output, that's why it was 12.5 volts. You had the tach wire on the wrong connection. It should be on one of the yellows as shown by the tach working now.

 

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OK so what do I do with the other half of the gray and yellow wires that are not attached to anything ? The original rectifier was 2 red to red, 2 yellow to yellow and gray to gray and black to ground.

 

[GA_Boater]

If you did one wire at a time from the old to new rectifier, how did you end up with left over wires?

Serial number? Consult you manual for a wiring diagram.

 

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It's a 6 wire rectifier P/N 883072T. There are 2 red wires,2 yellow wires 1 black and 1 gray. They match the same colors on the engine. The only reason to plug the gray into the yellow was to see if that would make the tach work. I would guess that there is not a pulse coming from the gray wire on the rectifier ?

 

[wrench 3]

It's a 6 wire rectifier P/N 883072T. There are 2 red wires,2 yellow wires 1 black and 1 gray. They match the same colors on the engine. The only reason to plug the gray into the yellow was to see if that would make the tach work. I would guess that there is not a pulse coming from the gray wire on the rectifier ?

I'd say that your assumption is correct.

 

[GA_Boater]

883072T is a regulator/rectifier. The grey wire is connected internally to one of the yellow wires. Try moving the grey wire to the other yellow wire connection and see if the tach works. I think it will or the stator is bad. I don't think it is because you wouldn't have the 14.7 volt output.

 

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Received the new rectifier today. Install it and tach works and batteries are charging. Thanks to all !