Tach not working, not showing sufficient charge 1996 Mercury 115hp 2 stroke

[Boat called Bertha]

Discovered this when launching boat yesterday. Brought boat up river to the my dock. Fired kicker engine as well. Battery gauge showed a slight improvement. Battery is new Kirkland deep cycle. Ran some volt tests. With kicker only meter read 13.13 with slight increase in rpm. Fired the big engine, 13.02. With only big 12.07 @ idle. 12.09 down to 12.02 with increased idle. 12.00 with more throttle. Remember tach not working so can't give a number; but all cylinders firing. (Also noticed last season that the tach would function and then drop to zero and then jump back up). Returned to idle 11.98. Both engines at idle 12.47. Kicker only idle12.57. Increased rpm 13.02.
I've looked at info regarding the stator, rectifier and regulator. Have not disconnected any wiring to test yet; just hoping someone could give the proper procedure for my 1996 Mercury 115hp 2 stroke engine. Our local marina is 3 weeks behind and we have company from Michigan arrive June 30 and hoping to go fishing on Lake Erie. Any advice is appreciated.
Thanks in Advance
John

 

[Little Richard]

Sounds like your rectifier. Google cdi electronics trouble shooting. Do some test in there with voltmeter. Dirty or bad ground or having a bad battery can cause them to go bad

 

[Boat called Bertha]

Thanks LR 4 the info.

 

[CharlieB]

The tach on most Merc outboards is actually a sort of volt meter. The increasing voltage with RPM.

The most likely problem is a blown diode in the rectifier but with all things electrical there is NO RETURN so you need to PROVE the fault before buying any electrical parts.

Disconnect the battery then remove the rectifier. Somewhere in the Sticky Posts there will be the directions how to test the rectifier using an Ohms Meter, or you can Google it.

Only after you have proven a bad diode should you order a new rectifier.

 

[Boat called Bertha]

Thanks Charlie B. My local marina will look at it on Monday, things have slowed for them. With the info I provided, they believe it's the regulator/rectifier. Your response is comforting that we are on the right track. Keeping my fingers crossed that that is the solution.

 

[Boat called Bertha]

Yes it was the regulator. Now there is a possibility that a deep cycle battery may be the cause of the regulator being "cooked". Now in saying that I've own Bertha for 18 years and always had a deep cycle battery to run the engine, fish finder, marine and am/fm radios. The regulator was the original one.
Has anyone any info regarding deep cycle/regulator situations?

 

[Little Richard]

Why did you replace the battery to begin with was the old one bad. I read a bad battery or poor grounds or dirty connections to ground will damage the rectifier. Something like if the battery is unable to take the load off the rectifier/regulator it gets really hot and damages it. So maybe there is a connection there to the problem.