# RPM metter & Voltmeter not working



## Star1pup (Aug 3, 2004)

I had new material put on my pontoon last winter to replace the carpet that was looking pretty bad. The guy I hired did a great job, but now the RPM meter & voltmeter are not registering. I suspect that when they put the console back on something was not wired right. He is going to come check it our for me, but I'm trying to learn a little myself so I can talk semi-intelligently with him.

I can see how the voltmeter works, but how does the RPM get from the motor to the meter through a wire? Any insight will be appreciated.


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## Misdirection (Jul 16, 2012)

I believe that the RPM's are measured off of the alternator. Purple wire if I recall correctly (need to check a wiring diagram). But I would also suggest checking your ground as well.

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## Workdog (Jan 10, 2007)

Your RPM meter, otherwise known as a tachometer,  should have at least four wires to it: black wire(s) for ground to and probably from the tach to other gauges, a red wire(s) to power the light bulb to the tach and probably from the tach to other gauges, a purple wire for +12 volt power to the tach (this one does not power the light bulb in the tach) to the tach and probably from the tach to other gauges, and a gray "Sig" or Sender wire. The sender wire comes from one of the voltage regulators, and is where the tach gets its signal for rpm.

Your installer may have not reconnected the wiring bundle from the engine electrical harness to the gauges. Alternatively, when the tach AND the voltmeter are not working correctly, you may have a bad voltage regulator on the engine that the gauges are connected to. If the voltage regulator (bigger engines have two...but only one voltage regulator will feed the tach) that feeds the tach is inop, then, you won't have a tach signal AND the battery won't be charged, hence the inop voltage meter. I hope your problem is in a disconnected engine wiring bundle.

So, how does a voltage regulator go bad? Sometimes they just fail...it is an electrical component after all. Sometimes, a console installer, when hooking power back up, momentarily puts the positive battery cable on the negative post, and the negative cable on the positive post, thus frying the voltage regulator. A way to check if the voltage regulator is working is by running the motor, and checking the voltage output at the pos and neg posts on the battery. If the Voltage regulator is working, you should read 14.5 volts or so across the pos and neg posts on the battery.

If your engine has an alternator, the feed for the tach will come from the alternator, but the wire will still be gray. 

Sometimes, the fuse on the end of the wiring harness in the engine compartment, that services the voltage regulator or alternator that is connected to the tach, blows. You should check to see if you have any blown fuses under the engine cover.


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## Star1pup (Aug 3, 2004)

Wow! I always get an education on OGF site. Thanks!

BTW: The motor is a 9.9 Mercury 4-stroke Bigfoot.


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## Workdog (Jan 10, 2007)

Star1pup said:


> Wow! I always get an education on OGF site. Thanks!
> 
> BTW: The motor is a 9.9 Mercury 4-stroke Bigfoot.


I believe on that motor there is one rectifier/regulator and one inline fuse at the motor. If you search online, you can come across a free service manual. Hopefully your problems are with a disconnected harness or wiring at the console.

P.S. Here is a soft copy of your service manual: http://1manual.com/Mercury manuals/Service Manual PDFs/FourStroke/856159r1/cover.pdf Go to the bottom of the page and click on the outline entry you choose to read about.


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## Star1pup (Aug 3, 2004)

Thanks, Workdog. I was able to print out a wiring diagram and a wiring location diagram. It looks like the 20amp fuse is in the wiring to the starter solenoid instead of the rectifier/regulator, but I'll check it anyway.

I'll also check the voltage over my battery terminals while the motor is running as you suggested.

I'm beginning to think that the problem is either beyond the motor and in the boat wiring, or the regulator is kaput. The boat is on its trailer at the top of my drive and the guy who did the floor will be in the area this weekend and will take a look. I feel confident in his ability so hoping for the best outcome so I can go fishing.


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## Star1pup (Aug 3, 2004)

The situation has been resolved. The guy who installed the new floor covering came down on Sunday because he knew I wanted to launch. He found that there was one wrong hookup that he changed and now everything works great.

I really appreciate someone who corrects a problem like that and I'll use him again whenever I need a good mechanic.


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