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Discussion Starter #1
I have twin merc 150 blackmax 1993 engines. Port tachometer stopped functioning. When I got home I hooked the starboard engine leads to port tach and the port tachometer worked fine, but still will not work when connected to the port engine. I then check the voltage coming from the port engine across the leads and got 12.5 volts, the same voltage readings I got from the starboard engine. So now I am lost on what to do. Is the tach sending unit on the starboard engine bad? If so, where is it located? Any help would be greatly appreciated. Thanks, Karl
 

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According to your post, the port tach quit working- you then hooked the starboard engine to the port tach and it worked okay.
Try hooking the port engine to the starboard tach (assuming the starboard tach was okay originally), if the starboard tach registers then, I wouldn't know what to say. If the starboard tach doesn't register, I'd say there is a problem in the signal from the port engine to the tach.
 

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Thanks for the response Mikie. Neither tachometer works with the port engine. Both tachometers work with the starboard engine. The voltage at the tach wire from each engine is about 12.5 volts so there is power coming from each engine. I don't know where the tach sensor is located. Is it on the voltage regulator. Karl
 

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There is no tach "sensor" the tach lead is the grey wire in the harness, it is connecter to the alternator output ,usually at the regulator,or a junction block that also contains the alternator output,,the tach reading depends on the alternator & regulator functioning properly,it reads alternator pulses. assuming that your wire harness is good,,you probably have a charging problem. at idle speed, Outboard alternators put out very little charge,hence your 12.5 v reading. that's just your battery voltage. increase your rpm's and you should see your voltage increase if your alternator is charging,,if no increase then you are probably not charging. hence no tach reading.

if your motor is charging,and the tach checks out ok,then you need to look at your wire harness.
 

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Discussion Starter #5
Thanks RJ, That is what I was wondering, where the tach got its signal. My batteries seem to be charging properly, the voltmeters are reading about 14.5 volts when the engines are running and I get the same voltage reading when I hook the multimeter directly to either battery. There is no problem starting either engine. I will check the gray wire to the voltage regulator. I guess I could swap the voltage regulators and see what happens also. Do you think I could be having a problem with my stator? Thanks, Karl
 

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I suppose the stator is a possibility buit from my experience it is almost always the voltage regulator, and in a few cases the altenator. When it has been the altenator it was very obvious it had been wetted with saltwater.
 

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To check if your port engine is charging - don't start the starboard engine (you know it's working) - then check your battery voltage with just the port engine running.
 

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It was the top voltage regulator. The hose that runs across the top of the head sprung a leak and was spraying hot steam onto the voltage regulator and melted it. The leak is now fixed and a new voltage regulator installed. Tach now works. Thanks for all the help. Karl
 

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Now if someone could just tell me what's wrong with the tach on my diesel!!! [grin] Glad you got her working.
 
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