Logo
FULL SITE MENU

1990 90HP Tacho stops working intermittently

R

rude70

Contributing Member
Hi the tacho works at idle fine, then I will be cruising around 3000rpm and the tacho drops to zero. Now and again it works again when running. The engine had the water cooled regulator/rectifier that some one has disconnected and replaced with the small round silver item with one red and two yellow wires ( i believe is a half wave rectifier!).
I was reading a thread where someone said that if the tacho grey wire was connected to the yellow rectifier wire & the yellow stator wire, then it would not work when over voltage occurs since the rectifier grounds this signal - this makes sense. The problem is that my rectifier has two yellow wires with no grey trace on one of them. Each of the yellow rectifier wires is connected to each of the stator wires, the red wire is connected to the +ve circuit. At 1500rpm there is approx 13.5v from the red wire! The rectifier has no markings and I have also read that it does not matter which wire the tacho grey wire is connected to! I have tried two tacho's and they both do the same thing! Also I am a bit concerned since I have a maintenance free battery and posts say that you should not have this in this set up.
I have just swapped the rectifier yellow wires but cannot test for a bit. Any advice is welcome, thanks
 
ok..lets recap what probably happened...the motor charging system and the tach quit working...someone went cheap and put a rectifier in it..the tach works sometimes now and some times fails...does the charging circuit also fail at the time of the tach failure?..what is the reading in dc volts on your console meter or with a meter across the battery post read at the point of tach failure?

you are correct in you should not have a maintenance free battery in a rectifier only set up as you have now..the voltage output of the unregulated rectifier will go too high....in the 16-17 volt range and higher is common...what eventually will happen is the rectifier will blow ....before it blows you will usually see the tach cut up with varying symptom..

if it was my motor i would replace the rectifier with the proper part...take your motor serial number and go here http://www.marineengine.com/parts/mercury-outboard/index.php and get some idea of the part and cost...
 
Good advice above. But those water cooled regulators are a lil pricey, least last I checked.

Another, less expensive option is to run one'a this style regulator:

Show up often on ebay.
 

Attachments

  • RegulatorOldSchool.jpg
    RegulatorOldSchool.jpg
    79.7 KB · Views: 131
Thanks for your advice, I am in Australia so every part is expensive! It looks like a regulator will only be a few bucks less that the rectifier/regulator #0585195. I have a schematic diagram from a Clymer manual that is not good! The rectifier/regulator has 5 wires from what I can see from pics on the web (CDI unit is below). 2x yellow (for stator connections), 1x grey for tacho, 1 x red charging to starter solenoid, 1x purple for accessories to power tacho & gauges - is this correct?
193-4204.png
 
Sounds like. Right number of wire's & right colors ...

CDI has always been good to me. My latest project has all CDI ignition. Stator, timer base, powerpack, etc. Good stuff.
 
I have been following the wiring schematic and can see that the purple accessory/overheat horn +ve feed wire is fed from the A terminal from the key switch (when switched on) , which takes power from the red/purple +ve from battery attached to the key switch. Is the rectifier/regulator connected to the purple accessory cable to supply additional power when running? Is this the only purpose?
Thanks
 
The purpose of the purple wire from the ignition switch to the regulator is to turn the regulator on so it charges.
 
Back
Top