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Author Topic:   Mercury 60-HP: Stator Yellow Wires Hot
crabman63 posted 06-14-2008 10:38 AM ET (US)   Profile for crabman63   Send Email to crabman63  
I own a 2001 Bass Tracker-brand boat with a Mercury 60-HP outboard. I found [a problem] between the stator and the rectifier and [voltage regulator]. The yellow wires coming from the stator to the rectifier are hot and melting at the connectors. The green-white wires from stator are fine. The two red wires and grey wire from rectifier are fine. Not sure if [the rectifier and voltage regulator are] bad. I notice that Tachometer jumps around. Any suggestions what is wrong? I never had a problem with this motor. Also, according to the gauge the amp meter is still charging.

Crabman 63

[Editor's note: This was the only article ever posted from this user. He received a great deal of excellent advice, but never returned to acknowledge the advice or to provide any sort of follow-up information on this situation or problem. We have no idea if he even returned to read the replies.--jimh]

jimh posted 06-14-2008 12:52 PM ET (US)     Profile for jimh  Send Email to jimh     
If your Mercury 60-HP motor is being asked to continually supply high amounts of charging current to your vessel electrical system, such as might be needed to recharge batteries used for operating an electric trolling motor, the heat being generated in the process may be causing the damage you report on the yellow wires. The YELLOW wires are most likely the stator winding which supplies the alternator which charges the battery and supplies the engine with electrical power. Once connections become hot, the connections tend to increase in resistance. This causes them to get hotter due to the voltage drop which occurs across them as current flows through the connection. You may need only to repair the connection and replace the existing connectors with new ones.

I am not clear on how you made the deduction that the engine charging system is operating correctly. What is the output voltage from the engine charging system when the motor is operating above 1,500-RPM? Please measure the voltage with an accurate meter to 0.1 volts resolution. Thanks.

jimh posted 06-14-2008 12:58 PM ET (US)     Profile for jimh  Send Email to jimh     
The tachometer signal is supplied from a half-wave tap in the alternator rectifier. Erratic operation of the tachometer is often a sign of a problem in the rectifier.
jimh posted 06-14-2008 01:01 PM ET (US)     Profile for jimh  Send Email to jimh     
The voltage regulator in an outboard motor is designed to limit the output voltage from the motor's charging circuit to approximately 14-volts. If the voltage regulator fails and the charger output voltage is not regulated, it is possible for the charger output voltage to rise above 14-volts. As the voltage output from the charger rises, this will tend to cause more current to flow into the boat's electrical system, and this current is typically absorbed by any storage battery connected.

A failure of the voltage regulator can lead to excessive charging current. This can, in turn, lead to a failure of the rectifier or the stator.

jimh posted 06-14-2008 01:37 PM ET (US)     Profile for jimh  Send Email to jimh     
It is fairly common that the rectifier and the voltage regulator are combined into a single un-repairable assembly. If there is a failure of either, you have to replace the entire assembly.

If the rectifier and voltage regulator are separate assemblies, you can repair them individually.

In making repairs to an outboard motor's electrical charging system, it is important to properly identify the actual cause of the failure and all the failed components, otherwise you can quickly destroy a replacement part if there are still other bad components in the system. (This is why electrical parts are seldom if ever returnable to the part seller.)

Moe posted 06-20-2008 07:30 AM ET (US)     Profile for Moe  Send Email to Moe     
There was a recall on the 60HP BigFoot on our 2003 150 Sport. If I recall correctly, it was the rectifier or voltage regulator. The recall warned that not having it accomplished could result in a fire under the cowling. You need to contact Mercury and see if your motor serial number is one of the affected models.


jimh posted 06-20-2008 09:26 AM ET (US)     Profile for jimh  Send Email to jimh     
Moe--Thanks for that information regarding the service bulletin or recall on the Mercury 60-HP Bigfoot motors. If the originator of this discussion is still participating, I am certain he will find that valuable, although he has not responded to questions and may no longer be involved. In any case, it is excellent information, and it will be valuable to anyone who reads this discussion.
billsa posted 06-22-2008 09:56 PM ET (US)     Profile for billsa  Send Email to billsa     
I have a 2003 150 sport with a 60 hp EFI four stroke bigfoot as well and did not recieve a recall from Mecury. I did buy the boat used in 2004. Did Moe's dealer fix the problem at no charge? I will call the Local Boston Whaler dealer tomorrow. Thanks for the heads up.
jimh posted 06-23-2008 09:34 AM ET (US)     Profile for jimh  Send Email to jimh     
It is unlikely that a manufacturer keeps track of their motors when ownership changes hands, unless there is some specific registration or warranty extension paperwork involved. Notice of Mercury's recall of their motors with defective voltage regulators was first given on CONTINUOUSWAVE some time ago by vink, in

According to a listing on an Australian government website the affected Mercury motors with the potentially hazardous voltage regulator defect are:

Product Info:
Model: Mercury/Mariner 30/40 3 Cylinder Four Stroke - Model year 2002 and 2003. 0T438281 through 0T800906. Belguim 0P156468 through 0P269818.

Mercury/Mariner 40/50/60 4 Cylinder Four Stroke - Model year 2002 and 2003. 0T416659 through 0P800906. Belgium 0P156559 through 0P270043.


Inasmuch as in another discussion an owner reported that Mercury replaced for no charge the defective regulator along with a great deal of other components which were damaged by the regulator's failure, I think it is a reasonable assumption that replacement of the regulatory will be at no charge.

Given the potential for extensive damage--there is a report of a Mercury motor catching fire--to your Mercury motor if this component fails, it is prudent to consider replacement of it even if you have to bear the cost. However, I suspect you will not be charged.

billsa posted 06-25-2008 01:59 PM ET (US)     Profile for billsa  Send Email to billsa     
I took the boat into the local Boston Whaler dealer, and they are going to replace the voltage regulator at no charge. Thanks for the information. I would have been completely in the dark if I had not seen it posted here. Thanks again for the information and time spent researching the past threads pertaining to this particular situation.
dinodog posted 03-29-2010 05:35 PM ET (US)     Profile for dinodog  Send Email to dinodog     
Hello. I too have a 2003 [presumably MERCURY] 60-HP EFI FOURSTROKE, and my regulator failed last January 2010. I had it and a few other parts replaced for free by my local dealer. There was a cooling plate that the regulator bolts onto; it was replaced too. And also a temperature sensor and sender, so says the workshop dude.

I have lost some top end speed and my motor will now only rev out to 5,400-RPM. Top speed is now only 44-km/hour. Before the regulator blew, my boat would rev out to 5,800-RPM and travel at 50.5-km/hour, as stated by my onboard GPS-plotter and the [tachometer] guage. Since having the replacment regulator, I now rev out to 5,400-RPM and top out at 44km/hour; nothing else has changed. The engine purrs like a kitten, doesn't miss a beat but my top end speed is now down.

Would anyone have any suggestions?

There are no audible alarms and the charging circuit is now fully functioning. Would the fitting of a new regulator have anything to do with max RPM at load? I have booked the boat back into the workshop that replaced the regulator and they will put the diagnostic computer onto the computer engine management system. They tell me that this should see if there has been any alarms or drop in RPM. Anyone know more about this? Has anyone who has had the regulator replaced had any drop in performance? Has the regultor got an in-built rev limiter?
Thanks for your time guys.

jimh posted 03-29-2010 09:55 PM ET (US)     Profile for jimh  Send Email to jimh     
The electrical system on a 60-HP motor is probably rated for a charging current of 25-amperes. That is just a guess; I don't know the exact rating for your motor. With 25-amperes and 15-volts, the power is 375-watts or 0.375-kW. We compare this with the engine power output of 60-HP:

0.375-kW x 1-HP/0.750-kW = 0.5-HP

This means that at maximum charging current the electrical system produces only a 0.5-HP equivalent of electrical power. Even if we consider the electrical charging system to be very inefficient, say only 50-percent efficient, this implies a drain on the engine of only 1-HP.

I do not think that a 60-HP engine which was bogged down to 59-HP by an electrical load would show a great deal of change in the maximum engine speed at full throttle. Your narrative gives 400-RPM drop at full throttle. It seems like that is too much to account for only 1-HP influence from the electrical load. Even more important, the prior engine speed was not produced with no electrical load, so it is even more unlikely that the change in the charging system components would have caused the drop in engine speed. At least there is not a good basis to think they would based on the power being used in charging.

In situations where there is a malfunction, it is hard to predict exactly how the malfunction will influence the system. It could be the rectifier has another way to influence the engine speed.

dinodog posted 03-30-2010 06:05 PM ET (US)     Profile for dinodog  Send Email to dinodog     
Are you saying that maybe the rectifier circuit could somehow influence [the top speed the engine can reach]? Possibly? The regulator and rectifier are contained within the same sealed unit. When [the sealed unit] is changed, they are both changed. With the regulator being the only major thing changed to my outboard, it is the logical point for me to start an enquiry as to why the top end speed has dropped, as it occured around the same time. When you have something replaced free of charge by a dealer, they are reluctant to give you any information about what was done and what parts were changed. I didn't even get a piece of paper from them to tell me that it was replaced. I knew it was, but I have no documentation to tell me so. I have since found out that a temperture sensor and sender was also replaced as part of the job bulletin that came to the dealer from Mercury. How can one trust someone who is reluctant to give any information about what happened to my engine? It is mine, I own it, but I can't find out what they did to it.

So anyway, [another visit with the mechanic] is booked back in, but I don't trust them. I'm guessing it will cost me plenty so I'm hopefull of tying the problem to the change of regulator, but they will try to tell me different and possibly throw lots of parts at it that may not change a damn thing.
I'll report back when i have it looked it.
Thanks for your time and information.

jimh posted 03-31-2010 07:37 AM ET (US)     Profile for jimh  Send Email to jimh     
As I mentioned above, the maximum mechanical load imposed on the engine by the electric power created in the charging system is limited to about 1-HP. The charging system, when producing its maximum electrical power output, might rob about 1-HP from the engine, which otherwise develops 60-HP.

We now judge if adding an extra load of 1-HP to the engine would cause its maximum speed under full load of the boat to decrease to 5,400-RPM from its previously noted maximum speed of 5,800-RPM. I do not think this is reasonable. The basis for my judgement is as follows:

The engine speed at maximum throttle with a fixed load is generally an indication of the maximum power being produced, so we can say that the faster the engine can turn under a fixed load, the more power it produces. If we note a decrease in engine speed under the fixed load, we assume less power is produced in the engine. If all else remains the same, and we test the engine speed in two circumstances, the case where the engine speed runs lower is assumed to represent less power being produced. We can then say, reasonably, that power is proportional to engine speed.

If we allow that 5,800-HP was indicative of 60-HP, we can estimate the power produced at 5,400-RPM using a simple linear ratio. We find that

60/5,800 = x/5,400, where x is the power at 5,400

Solving for x we get 55-HP

If 5,400-RPM at full throttle represents only 55-HP, this is too much loss of power to attribute it to the added load from the electrical system when operating at its maximum rating.

There are another possibilities to explain the observation of a change in engine speed: test error or measurement error.

Test error could result if the test conditions were not well controlled. It may be that other factors influenced the test, and the observation of a 400-RPM drop in maximum speed was caused by factors other than the replacement of the rectifier assembly.

Measurement error could result if the engine speed measurement was not made accurately or consistently. A source of error in the engine speed measurement is very likely in this situation because of a very close association between the measuring instrument--the tachometer--and the device under test--the rectifier.

The tachometer on most outboard engines is fed a signal from the engine's charging system. The signal comes from the rectifier. If the rectifier is malfunctioning, there is a possibility that it could affect the reading of engine speed shown on the tachometer. Therefore, an alternative explanation of the data presented in this narrative--the 400-RPM drop in engine speed--is to find that the engine speed has not actually changed, and only the indication of the engine speed on the tachometer changed, due to the influence of the rectifier on the signal sent to the tachometer. This theory could be substantiated in two ways:

If the data collected during testing included boat speed at maximum throttle, we should find that the actual speed of the boat did not change, or changed only very slightly. The actual speed of the boat is also a direct indicator of engine power output. If the boat speed stayed the same, it would imply a measurement error in the tachometer itself.

We have measured the engine speed with two different rectifiers. To evaluate if there is any change in the accuracy of the measurement with change in rectifiers, we need a third tachometer. Connect this third tachometer to the engine. Then repeat the tests. Compare if the readings of the third tachometer confirm that the engine speed changes when the rectifier is changed, then we have more confidence that there is an actual change in engine speed and not a measurement error.

jimh posted 03-31-2010 07:42 AM ET (US)     Profile for jimh  Send Email to jimh     
ASIDE: The duplicate discussion begun on this same topic by reviving another discussion which had been dormant for five years has been deleted. We have a very strong preference for not engaging in multiple threads to discuss a single topic.
dinodog posted 03-31-2010 06:03 PM ET (US)     Profile for dinodog  Send Email to dinodog     
Boat speed is being measured by an onboard GPS plotter. This I would deem to be fairly accurate. Also, speed decrease has been noted on the onboard analogue gauges, now showing about 26-MPH, which is fed (water pressure) from the speedometer tube mounted in the bottom of the leg. Cheers
jimh posted 03-31-2010 07:43 PM ET (US)     Profile for jimh  Send Email to jimh     
Is the boat speed measurement controlled for influence of current, wind, and waves?
dinodog posted 04-11-2010 10:47 PM ET (US)     Profile for dinodog  Send Email to dinodog     
[O]f course speed is influenced by waves, wind and current. But last week, with flat glass water, no wind and top of the tide, top speed is down 7-KMH and [engine speed] was solid at 5,400-RPM. I know no one is able to tell me why, I get that. Just looking for possible answers. [The cause of the decline in top speed for the boat and the engine has] to come back to the replacement of the regulator. This is and has been the only major repair that this engine has ever had. Are there any Mercury mechanics out there that have done the modification for the replacement of the regulator? What do you touch on the motor and what do you replace? I hope I don't get ripped off at the check out when the boat goes back to the dealer and they try to palm off [the cause of the decline in performance of the engine] with something else that they say is at fault. Is it possible that the torque curve has changed due to some replacement part that is, the temperature sensor or the cooling exhaust plates? Do you have to remove the throttle cable during this fit-out? Was the computer reset to factory defaults? Any input is highly welcome. Thanks for reading. Cheers.
jimh posted 04-12-2010 08:35 AM ET (US)     Profile for jimh  Send Email to jimh     
If you think the throttle is not opening all the way, you should be able to check that yourself without much trouble. Remove any air baffle or silencer box that covers the throttle bore, until you can see the throttle plate. Then move the remote throttle lever to maximum throttle. See if the throttle plate opens to the full position.

It would be unusual for a replacement of the rectifier assembly to affect the throttle linkage. I don't think you need to perform much disassembly of the power head to replace the rectifier assembly.

dinodog posted 04-12-2010 07:51 PM ET (US)     Profile for dinodog  Send Email to dinodog     
[I] too thought it would be unusual to remove the throttle linkage for such a job.[Long pejorative oration about his dealer deleted.]
jimh posted 04-12-2010 10:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Dino--We are interested in your electrical problem. Let us know when we can help you with more electrical problem solving. No more dealer bashing essays, please.

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