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Author Topic:   Inoperative Tachometer
Mister S posted 04-26-2006 02:07 PM ET (US)   Profile for Mister S  
The tachometer on my boat doesn't work. I've read that the signal comes from the rectifier [and is carried on a] gray wire. Can I simply switch from one rectifier to the other? Are they identical? Any help would be appreciated.

Dan S.

jimh posted 04-26-2006 07:33 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't understand your question. Most outboard motors only have a single rectifier assembly which is associated with the battery charging circuit and from which the signal for the tachometer is derived.

What is this second rectifier of which you speak?

phatwhaler posted 04-26-2006 09:52 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
IF you have a older V6 Merc then you have two regulator/rectifiers. The charging system has two 20amp circuits that both tie into the starter solenoid. Each regulator has a grey wire that can provide a tach signal. If your tach is not working you need to switch to the other regulator's grey wire and see. I would run the boat and disconnect each regulator one at a time. Make sure your tach is working and that the charging system is working. I just went through all of this on my boat.

What make and model is your motor?

pw out.

Mister S posted 04-27-2006 02:30 PM ET (US)     Profile for Mister S    
I should have included - 1994 Mercury 200 carbed offshore model.

PW, I haven't been able to check motor since I came up w/ this question. Do both rectifiers have the gray wire going to the solenoid or is one unused? Can I run the motor w/ just one in service?
You also gave me another thought - the starter is sometimes very weak, barely turns over. Hit key again and starts, may be related?

Dan S.

phatwhaler posted 04-27-2006 04:39 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     

Each regulator has two yellow wires that run to the stator, two red wires that connect to the starter solenoid, and one grey wire that connects to the tach wire.

So that's a total of four yellow wires to the stator, four red wires to the solenoid, one grey wire to the tach, and one grey wire with a black plug in the end. (Not being used) There are no grey wires going to the solenoid. You can run the motor off one regulator and totally disconnect the other reg. The difference is that there will only be 20 amps of charging power instead of 40. In the factory service manual (FSM) diagnostic procedures in explicity state that you need a known charged battery and good connections to diagonose regulator issues.

Here's what I would do:

1. I would make sure you have a known good battery (charged) with clean electrical connections.
2. I would run the boat (@>1200 rpms) on each regulator separately and take note of voltage. I would measure that voltage at the starter solenoid with a digital voltmeter. Actually run the boat at about 4500 rpms with someone helping you. Make sure the motor is charging to around 14 volts. (Give it a couple of minutes for the voltage to build up). If you have voltage below 13 volts or above 15 volts you probably need a new regulator. Again I would check this with each regulator separately. Here's the problem with this little experiment. It may take a while for the engine and regulators to get hot enough to rear their ugly heads. When mine were giving me problems it took a while before they would start overcharching.
3. If you end up needing a voltage regulator I would buy two of them and install them both. If you have one that is still good keep it for a spare.
4. The regulators are a known weakness in an otherwise very reliable electrical system. Evidently Mercury has redesigned them a few times. They are not water cooled either like some other brands.
5. There are aftermarket regulators available from a company called Rapair or CDI Electronics. You probably need part number 194-5279. They're much cheaper than Mercury regs.

Hope this helps , you may just have some corroded wires that need attention.

Also, if you run the boat with disconnected wires, make sure they are taped you so you don't shock yourself, or damage something.


jimh posted 04-27-2006 08:07 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't understand how the solenoid--I assume you mean the starter motor solenoid--has come into the discussion of the tachometer. The two are not related in any way I can figure.
phatwhaler posted 04-27-2006 09:07 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
The battery side of the starter solenoid is where the idividual red regulator wires and the battery cable meet. This is how the batteries are charged.

phatwhaler out.

jimh posted 04-28-2006 02:40 AM ET (US)     Profile for jimh  Send Email to jimh     
It sounds like the solenoid terminal is used as a convenient wiring point to collect several conductors which connect to the battery positive.
Mister S posted 04-28-2006 11:11 AM ET (US)     Profile for Mister S    
PW, Thanks for the great reply and info. I'll run tests over weekend. Low rpm test only as boat still on trailer, should still be able to get enough info. Thanks again.

jimh - thanks for help. This 2 rectifier set-up is a bit different.


cayollc posted 04-25-2008 11:54 AM ET (US)     Profile for cayollc  Send Email to cayollc     
I have the same problem on my Mercury 150HP (carburator) for 2 years. Tachometer not working. Would these instructions apply?

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