1986 Mercruiser 140 Elec. problem

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brs517

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Can anyone help me with this problem?<br /><br />Battery was dead on the water last weekend. I got a jump start and it ran just fine to get it home, but dead again once I shut it off. Hooked up my volt meter to the battery and it shows about 12.6v when not running and 12.5v when the engine is running. So, it's not charging, right?<br /><br />What I've done so far:<br /><br />Took battery in to be checked-OK<br /><br />Alternator & Voltage Regulator checked OK <br /><br />Belt tension OK<br /><br />Checked my connections, and cleaned the ones that looked even slightly corroded<br /><br />Checked Ohms on the main output wire from the alternator to the positive cable to the battery...read at about 4.5 ohms...that's ok, right?<br /><br />I'm running out of ideas!!! Can anyone help??<br /><br />Thanks,<br />Brian
 
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Trent

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Re: 1986 Mercruiser 140 Elec. problem

How was the regulator tested?
 
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brs517

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Re: 1986 Mercruiser 140 Elec. problem

I took the whole thing to an alternator shop...they said that they tested the alt. through the regulator, and that they were both OK.
 
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Trent

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Re: 1986 Mercruiser 140 Elec. problem

Disconnect the purple wire on the back of the alternator. With the key on do you have 12 volts on this wire?? (Not the alternator side but check the harness side)
 
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brs517

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Re: 1986 Mercruiser 140 Elec. problem

Yes I do. <br /><br />Key off:<br />Red wire=12.0v<br />Purple wire=Ov<br /><br />Key on:<br />Red wire=12.0v<br />Purple wire=12.0v
 
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Trent

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Re: 1986 Mercruiser 140 Elec. problem

Ok...<br /><br />1. Connect positive voltmeter lead to regulator terminal on alternator and negative lead to a ground terminal on the alternator.<br /><br />2. Turn ignition switch to "ON" position and note voltmeter reading. Reading should be 1.5 to 2.5 volts.<br /><br />3. If no reading is obtained, an open exists in alternator excitation lead or in excitation circuit of regulator.<br /><br />4. You already checked for voltage on the purple (harness side) Now check alternator side of purple. If you now have battery voltage on the purple your voltage regulator is bad.<br /><br />Try these things... If you still have problem their are a few other test to do.
 
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brs517

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Re: 1986 Mercruiser 140 Elec. problem

Hey Trent, I'm afraid I'm a little lost. What exactly did you mean by the "regulator terminal on alternator?" Do you mean one of the wires going into the regulator?<br /><br />I've got a Mando alternator, and if I'm not mistaken the regulator is attached to the back of it, inside a tin box (that has the red and purple wires going into it.)<br /><br />Thanks for your help (and patience!)<br /><br />Brian
 
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Trent

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Re: 1986 Mercruiser 140 Elec. problem

Yep...Those are the wires Im talking about.
 
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brs517

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Re: 1986 Mercruiser 140 Elec. problem

FIXED!!!! :D <br /><br />As it turns out, the orange wire was almost totally corroded within its insulation, about 1/8" back from the connection. I cut the bad part off, put a new connector on it, and now it works!! Charging about 14.4 while running...much better! <br /><br />Thank for your help Trent!
 
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Trent

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Re: 1986 Mercruiser 140 Elec. problem

Glad you got it... Aint it fun when you do stuff yourself! :)
 
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brs517

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Re: 1986 Mercruiser 140 Elec. problem

Most definitely! And the best part is that I fixed it for $1.29!<br /><br />Thanks again!
 
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