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Mercury 90HP not charging

jim_d

New member
"Hi all. I have a 90HP 2cy ser

"Hi all. I have a 90HP 2cy serial 0T734284 that does not seem to be charging. The battery voltage is 12.8 when the engine is not running. When the engine is running, the voltage does not change. The manual says the voltage should increase to around 14.5. Coincidentally, the tachometer no longer works and moves erratically on the dial.
(Not sure if the two problems occurred at the same time.)
I'm thinking I need a new regulator and a new tachometer.
What do you think?

Thank you!

Jim"
 
"Test your rectifier/regulator

"Test your rectifier/regulator according to your manual. The problem you are describing is typical of blown diodes in the rectifier. If you have ever created a spark or connected the battery up backwards (even for a split second), you blew a diode(s)."
 
"Well, yesterday I replaced th

"Well, yesterday I replaced the OE regulator with a Sierra replacement. (Courtesy of marineEngine.com)
The good news is that the charging system is working properly now. At cruise speed, the battery is being charged at 14.5 volts.
The tachometer is also working...sort of. Although the tach reading is now steady, it reads on the high side. At idle, it reads 1200rpm and at WOT throttle the needle pegs to 6000rpm. Not sure if I can simply recalibrate the tach or it needs to be replaced. Any ideas?

One other thing...the Sierra replacement part only came with five connecting wires. The OE part had six. A note in the box said that a sixth wire on the Sierra was not necessary since it grounds itself through the metal housing and the motor bracket. Problem is that the motor bracket on my motor is plastic. I had to run a wire from the Sierra regulator housing to the clipped ground wire on the OE reg.

Thanks for all previous advice.

Appreciate it if anyone has any info on the current state of the tachometer.

Thanks!!!"
 
Look on the back of your tach

Look on the back of your tach and make sure it is set exacly on 6P. Close don't count.
 
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