View Full Version : Tachometer Troubleshooting

john Thomason
10-17-2002, 07:56 PM
I have a 1985 Johnson 40. The tachometer is new but doesn't work. I have 12 volts and a good ground. How can I tell if I am getting a signal from the grey tach. wire

10-17-2002, 11:13 PM
"John... It would have been better if your question was in the outboard section rather than miscellaneous as I just stumbled over it here. Usually that type problem is due to a shorted blown rectifier. Test it as follows:

Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier


john Thomason
10-18-2002, 11:14 AM
" THANKS Joe, I did as you said in your instructions. I am not an electrician, but I found a reading on the ohm meter any way I connected. The alternator is charging. What does the rectifier do? The original question was my first post, I wasn't sure where to post this problem. The tach. "grey wire" from the terminal post, on the motor, is going to the tachometer. From this information, can I be reasonably assured that the rectifier is the problem? THANKS AGAIN FOR YOUR HELP "

10-18-2002, 11:39 AM
"John.... If you obtained a reading at the rectifier on the ohm meter in both directions, it would be impossible for the charging system to be operational. The rectifier converts AC voltage that is coming from the stator to DC voltage which is needed to charge the battery.

The rectifier usually has a yellow/gray wire that attaches to the terminal strip at the engine, and the gray wire is attached to that same terminal. That gray wire is the one that leads up to the control console and is to be connected to the gray tachometer lead if a tach exists.

There are some rectifiers that do not have a yellow/gray wire but rather have two yellow wires, in which case, it doesn't matter which one connects to the gray tach wire.

Bottom line = If the rectifer doesn't check out exactly as I explained above, the rectifier is faulty. NOTE... before installing a new rectifier, make absolutely sure that the terminal where the RED rectifier lead connects to has "Positive" (+) voltage. The rectifier will not tolerate reverse voltage and will short out immediately if reverse polarity exists.


john Thomason
10-18-2002, 02:27 PM
" Joe---- I did the test you suggested ,again,and the rectifier checked ok. I used a different ohm meter. The tachometer I am trying to hook up, is a NEW FARIA. The boat has never had a tachometer but the console control has the hook-up. All these wires check good. I have two questions?

#1--Should the RED wire that feeds the rectifier have 12 volts constant without going through the switch? Mine does.

#2---Is there any way I can check this new tachometer before I send it back? I do not have, or know, where I can obtain another tach. for testing.
You have my GREATFUL APPRECIATION for the help you are giving me. "

10-18-2002, 06:09 PM
"John.... I'm not familiar with the brand "Faria". The tachs I've rigged have all been OMC tachs. In order for a tach to operate with a OMC outboard, they must be able to operate off of the engines 6 pulse charging system (rectifier) via the gray wire, and the back of the tach should have a dial that could be set to the number 6.

#1 Question = Yes, that wire always has 12 volts constantly assigned to it whether the key is on or off.

#2 Question = Sorry, I don't have an answer to that. I always have a spare tach on hand and use it as a test instrument.


john Thomason
10-19-2002, 02:02 PM
" Joe -- My tachometer has the following information on the back:
# Poles Set
I called three different dealers a got three different answers as to how many poles my alternator has. Does my 1985 Johnson 40 have 6 poles? I tried the tachometer on all the settings, with negative results. I figured if the setting was wrong, the gauge would read wrong. Joe, I have been a mechanic for over fourty years but this is my first experience with a pulse tachometer. THANKS FOR THE EDUCATION! "

10-19-2002, 09:00 PM
"John.... Nothing in the OMC manual states anything about "poles" pertaining to the stator. The only poles mention would pertain to the ignition sensor triggering magnets located in the flywheel and they have nothing to do with the tachometer.

Did that tachometer come with instructions that stated it would operate with your engine? If not, I'd suggest you return it and obtain one that's designed specifically for your engine.


04-15-2003, 03:35 PM
I am looking for tachometers for my 77 454 Mercruiser engines with thunderbolt ignition. I cannot get the teleflex to work because the old tachs run off the alternator. Where can I get some help?

Nick Seabridge
06-04-2003, 05:59 AM
I have two 1988 Mariner 40 outboards that are manual start and am looking to attach tacho's to each engine. According to the manual I have they have to be connected to the 2 green wires. Any ideas where I can obatin such tacho's ?

louis chandler
04-29-2004, 12:42 PM
" I sent a message about a 1991 200 HP Johnson GT outboard, and I'm not sure if it posted. The engine runs fine all day at half to two thirds throttle, but when I progress to full throttle, the alarm sounds after about 5 seconds. THe water pump seems to be working fine. Do you think I have an over heating problem, or could the engine just be turning too fast? How do I tell. Thanks again and I look forward to hearing from you.

Louis "

kirk rau
07-10-2006, 09:53 AM
"I have a honda 45 4 stroke that the tach stopped working. the clock on it works, If I disconnnect the gray lead the clock stops working. Does anyone have any ideas of why the tach does not work but the clock hour meter on the tach does.???? thanks kirk rau"

Tony M
02-04-2007, 11:43 PM
"I am considering buying a 1987 Searay Seville 19' boat with a 130 HP Mercruiser inboard/outboard. The tachometer was recently replaced with a new gauge, however, the tach is only registering up to 2500 rpm's and nothing over that. Why would the tach not function correctly at higher speeds?"

Karl Houck
03-25-2007, 08:55 PM
"Hi, I have a 1999 Crownline 225 with a 5.7 250 HP Mercrusier & Bravo III. My Tach was working ok last year at end of season. I have done several winter project this off season including Installing an Amp for the stereo and a Corsa Captains Call exhaust. Upon taking the boat out for a test drive and checkout run my tach is reading funny. It is reading high. Idle is reading 1100 RPM compared to last year of 800 RPM. The boat is reading 3900 RPM at 30 MPH compared to last year of 3300. WOT with the exhaust closed is reading 5300 RPM compared to last year of 4800 RPM. While crusing through a slow speed area and the motor at a constant speed the Tach would fluctuate between 1200 and 1800 RPM. Have I pulled something lose or got a lose connection somewhere? Is there a wiring diagraham that I could follow and check this out?"

Bill Neal
05-15-2007, 08:09 PM
Does anyone out there know how I can find or make a quick-disconnect flusher for my 1991 Johnson 200 that I can mount near the top end of the motor housing? I keep the boat on a lift and it's a serious pain to use the "ear muff" flusher on the lower unit.

Bill Neal
05-15-2007, 08:20 PM
"I've recently acquired a 1992 C-Hawk 25, powered by a 1991 Johnson 200 (Johnson 200 Model J200TXEIB.) I've installed a second helm amidships. I need to install a second starter switch at the new helm. No one seems to know definitively how to do that. Seems like OMC should have a pat solution, but I will be darned if I can find it. Is there some sort of kit that OMC makes to have dual helms and with dual starter switches?

If not, can anyone tell me how to wire that up myself? Seems like I would need a nominally closed relay to ground the stator, then activate the relay to open whenever I turned on the starter switch from either helm. Other's have said I need to wire in some diodes to make the kill switch work and prevent electrical feedback into the regulator. But no one cal produce a a wiring diagram or tell me what type of diodes I should use. I'm seriously stumped on this issue. Thanks for any help."

Tom W Lewis
05-17-2007, 10:27 PM
"I just got my boat back from the shop ,the heads were replaced and other work done , now my tachometer spins around clockwise all the way when the motor is started. (pegged) Has anyone ever experienced this? Any thoughts"

06-06-2007, 02:43 PM
Does anyone know how you determine the pulse from my 1988 4cyl Johnson 140hp engine. I'm install an new tach and need some help.

Todd Talbott
07-08-2007, 02:18 PM
"I don't know if I'm in the right place, but I am going crazy here with my Johnson 140HP 4 Stroke b/c it keeps blowing that little green 30A blade fuse on the engine every time I try to start it ... some clicking, like the battery is dead, then pop. I looked under the helm and two wires are hanging down from the ignition that go nowhere, a black one and a purple one. I don't know if they came loose or what, but they don't look like they were hooked up at all. Everyting was running fine and I think my batteries got low on power, as my charger was not working I found out a few days ago, but I put a good fresh charge on the batteries and all the accessories work fine. Anyone have a wiring diagram? It's got Bombardier on the back of the engine cover if that helps. Can someone give me any ideas?! I can't even find the serial number or model on the thing! It came with the boat used when I bought it, I was told it's a 2001 or 2003 but the guy was not sure. Thanks in advance ... I'm HIGH AND DRY till I fix this damn thing!! Thanks again!!"

Todd Talbott
07-09-2007, 10:18 PM
"I fixed my own problem. There was a wire (the "I" wire from the tach) and it was bare in a spot and touching a screw and grounding out. ALSO, I found the ground wire to my engine had come loose at the crimp point where it fixes to the bolt. These remedied fixed everything, back to HAPPY BOATING!! B/T/W, found the stickers, it's a 2003 Johnson 140HP 4Stroke, and I have all the wiring diagrams and everything now, so if anyone else has a problem, I'll be glad to share!!"

John C Jordan
04-11-2008, 01:06 PM
I need a tachometer for a 2 cylinder marine engine with a magneto. For a Kermath Atomic 2
If you know where I could get one I would appreciated very much. By the way I was told
that Teleflex does not make a Tachometer for
engines with magnetos.
Thank you

Thank you

John C Jordan

Michael Carl
05-01-2008, 09:49 AM
"I have a Mercruiser 5.7L Bravo III from 2005 in a Regal 2665. The Tachometer is not working and the Engine guardian straetgy reduces engine to 90 % of the power (according to the manual). Is it becourse the Tachometer is not working that the power is being reduced, and does anyone know what to do if the tachometer is not working. Is it a fuse? Anyone, ideas?

Best regards
Michael Carl, Copenhagen, Denmark"

05-04-2008, 01:44 PM
you need to plug it into a computor and find out

Mike C Chapin
07-10-2008, 05:51 PM
I recently bought a 96 Dynasty 180 with a 4 cyl volvo penta. the first few times out, the tach worked fine. The last time out, the tach read high as soon as I started the engine. It reads much higher than it was and when I throttle up to get on plane, it actually reverses and swings counterclockwise all the way around to the peg. All the connections on the back of the uage appear to be fine. i would check the other ends of the wires, but I'm not sure what they are connected to. I'm not sure if the tach is run by the alternator or what. It appears to be purely electrical in nature. No large cables to it, just some thin guage electrical lines. It's a faria guage for what its worth. Please help if you can"

Dwayne humphries
07-16-2008, 08:35 PM
"Hi i recently rebuilt my 1995 225 johnson oceanrunner piston & rings on one cylinder & just rings on two other cylinders runs fine at low to mind range but at 4700 rpm or over there is a alarm , beeping first then steady could this be a fuel restriction ? never had this problem before the rebuild do anyone have any answers"

12-09-2008, 02:24 PM
"I've got an 2002 baja. The tachometer quit working and there is no way to identify what brand the meter is. I have been in contact with Fountain, since they purchased Baja, and sent them pictures and they cannot identify it. I sent it to Livorsi marine and they had no idea what kind it was either. Any suggestions from anyone? Thanks"

12-09-2008, 06:30 PM
"Check out this site: He just might know what you have and could very likely fix it for you. Although he specializes in older instruments he does have an assortment of newer ones. He also converts older ones to new "techy" ones.
http://www.ccgauges.com/ ("")"

03-21-2011, 03:58 PM
[QUOTE=louis chandler;24233]" I sent a message about a 1991 200 HP Johnson GT


Check your power pack we had themsame problem on our 1991 Johnson 225
It turns out