2002 Mercury 75 2-stroke - replaced defective regulator and now have tach problems

[Bannister 6905]

My batt was not charging while the motor was running, so I replaced the voltage regulator with a compatible one from Amazon. This fixed the charging problem, but now, the tach is acting up. It reads OK up to 3000RPM, but as the engine revs, the tach does not follow - the needle also 'vibrates' within a range of about 100 rpm. Also, when I am running and raise or lower the motor trim, the tach needle temporarily rises, then falls back to around 3000. At what sounds like between 4500 and 5500, the tach needle actually drops to below 3000...weird. The battery is charging at just around 14V when running, which I verified with both the boat's voltmeter and my hand-held multi meter.

This is the second regulator I have tried to replace my original with - the first behaved similarly, except that after one trip, I found that one of the yellow wires coming from the regulator had overheated to the point that the protective sleeve was melted. I immediately removed that reg. and returned it for replacement. The second reg. has not shown that issue. All connections look fine.

I have considered rotating the pole setting switch on the tach to clear any corrosion, but it was working fine before I replaced the reg.

Anyone have an ideal as to what the problem (aside from yet another bad regulator) might be?

Many thanks!

Bannister

 

[Bannister 6905]

Anyone?

 

[flyingscott]

Are you getting the correct regulator or an off brand that they say is compatible? You could try a different tach a bad rectifier could have taken it out. If it worked before it should work now.

 

[Bannister 6905]

I am getting an "OEM-compatible" part and have confirmed it is designed to replace my failed OEM regulator. I ordered the replacement fro two different vendors. One came with 6 leads (with separate ground wire, just like the OEM), and it was causing the tach to act up. The second one was 5 wire, grounded through the mounting screws, and it has a similar problem, except it does not melt the wires. Both vendors provided replacements, which I have not tried yet. Both parts came in identical boxes and the aluminum cases looked identical, like they came from the same Chinese manufacturer (both had flash inside one mounting hole in the same position). Since I have no assurance that the "OEM" regulators don't also come from China, this was the least costly way to go. As I said, the battery charges at just 14V at full RPM, and I am not seeing any boiling of the battery at this point. I will probably try the 2 new regs to see if they perform the same way, but I'd really like to know why this is happening. There's nothing 'special' about the tachometer I am using - I'm sure there are millions of Teleflex tachs out there working just fine with a variety of regs / rectifiers.

 

[Bannister 6905]

By the way, I did rotate the pole switch several times, just to make sure corrosion had gotten to it. No change in how the tach acts with this rectifier...

 

[flyingscott]

Sometimes you get what you pay for.

 

[Bannister 6905]

Hmmmm....sounds like my rectifiers are about as valuable as your advice...

 

[flyingscott]

Hmmmm....sounds like my rectifiers are about as valuable as your advice...

Well at least I know the difference between a cheap compatible Chinese knock off and a direct OE replacement.

 

[Canufixit2]

Now Now .... Let's be civil. I for one would like to know the final result.

OP What brand did you buy in Amazon? Even some of the OEM is not made in the USA/