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Merc charging system

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sullybe

Contributing Member
I have a 1978 115hp inline 6 M

I have a 1978 115hp inline 6 Merc outboard. It seems to be running ok but when I check the battery I have 12 volts with the engin off and I have 12 volts with the engin running. I thought the battery would go up to 13.5 volts while the engin is running.Can someone tell me where to start looking to correct this problem. Also once the engin starts does it run off the battery or is the battery only to start it?
 
The engine does not charge at

The engine does not charge at idle. It will take 2-3 mins to climb into the "green" on cruise. The rectifier is a cube or module bolted on to the back of the cage. Two yellow wires lead from under the flywheel. These do go bad.
 
"Thanks Bandit,when you say th

"Thanks Bandit,when you say these go bad are you talking about the wires from the stator or the rectifier itself?"
 
"dan, The rectifiers will blow

"dan, The rectifiers will blow diodes if the wires make a bad connection, the battery cables are switched or left off, as well as other issues.

That motor will charge a bit at fast idle. Put a volt meter on the battery and read the voltage. Put on the flusher and push up the cold idle and start it up. At fast idle 1200+ RPM, you should see a rise in battery voltage. If no rise in voltage, the rectifer or stator is shot. It is most likely the rectifier. Rectifiers are available aftermarket. Try CDI.com"
 
"Thanks Chris,if the stator is

"Thanks Chris,if the stator is not working I didn't think the engin would start.I can see the engin running and the rectifer not charging.Will the engin keep running or will it drain the battery and just die."
 
"That depends on your ign. sys

"That depends on your ign. system. If it has the distrubitor on the side, than it needs the battery power to run. The ADI (Thunderbolt) stator had different circuits to run the the ign. and charge the battery. Your retifier is most likely bad. The stator can be checked with a DVOM on AC volts. Expect to see ~30 volts if the rectifier fails."
 
I put in a new rectifier and I

I put in a new rectifier and I have voltage slowly going up at a fast idle. I stoped watching it at 13 volts because the boat is in the yard and I don't like to run it to fast without a load on it. The new rectifier seems to work I had no voltage increase with the old rectifier.

Thanks Dan
 
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