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1977 merc 115 drains battery

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bayliner70

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"I have a 1977 nerc 115 that r

"I have a 1977 nerc 115 that ran great all day. then motor dies and can;t even jump it to start. Tightened up battery cables and ran motor next day and ran all day long. Took boat out today and didn't start. Had to jump and started right up. Stopped motor and wouldn't start again. Jumped, and then started up. stopped motor again and then tried to start but would not start or jump again. Replaced igntion coilcouple weeks ago. Just wanted to know why battery is running good one day and then the next nothing. Do I need to take battery out of boat after every use and charge? Or is there something wrong with charging system? Great compression, spark to all cylinders, power to every wire? Could you please help? Trying to get out and running before Tuesday. Thank you."
 
"Ed,

There is a problem wit

"Ed,

There is a problem with the charging system (stator/rectifier), or the circuitry.

Tony"
 
Before you get carried away ch

Before you get carried away check that it is not charging with a voltmeter. Then you need to test the stator and rectifier with a ohm meter to see which has the problem. Check all the connections for loose or broken wires. You do not just start replacing parts until you find the cause. You need to be sure that the new part is not going to get shorted out by some other problem. Good luck.
 
"Ed, The rectifier is a small

"Ed, The rectifier is a small rectangular chunk of plastic mounted on the front upright cowling support. Trace the two yellow wires (stator wires) from under the flywheel on the starboard side, and you will find it. As for your voltage issue. It sounds like the rectifier may be shorted to ground, causing your battery to run down. There is a test procedure for a Bridge Rectifier that you can try to see if it is broke.

You check two of the rectifiers terminals with an analog ohm meter(remove all wires). With the ohmmeter leads one way, you will have continuity, switch the leads and you will have no continuity. That is a good test. Any other result is a bad rectifier. The Stator wires are the AC terminals, the red wire is Plus DC and ground is Negative DC. The terminals to test are these pairs: (AC-Plus DC, AC-Ground, other AC-plus DC, other AC-ground). If these four tests all result in the good test, the rectifier is good. If you notice continuity both ways, or no continuity both ways on a terminal pair, the rectifier is bad."
 
"Would those same tests apply

"Would those same tests apply to my 1982 70 hp merc, s/n#7172524"
 
"I tried the above tests on my

"I tried the above tests on my rectifier, and found it to be bad. Thanks for your help.
The local dealer wanted $58 for a new rectifier ass'y. I went to the electronics store and bought one for $6, adapted it to fit, and it works good. The bridge rectifier I bought is rated for 40 amps and 200 volts."
 
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