1978 70 Johnson runs great but battery goes dead

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randycisme

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May 3, 2005
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I have checked all of the obvious wiring situations, if I charge the battery the motor will start and run fine, if I leave the battery hooked up to the motor without the motor running after a couple hours the battery is drained. Any ideas on what is causing this. I don't have any thing on the battery except the 70 and I cleaned all the wires to the solenoid and starter.
 
angus63

angus63

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Re: 1978 70 Johnson runs great but battery goes dead

Welcome!!!!!!!!!!<br />First, try a different battery to rule out a battery issue. Second, vigorously clean the terminals on the battery and the motor (+ and -) and use st.steel nuts and washers on the battery terminals (wingnuts don't cut it). Third, use a voltmeter to check voltage across the battery terminals running 2000 rpm + and with the motor off. How much difference is there? Finally, with the motor off, use an amp meter (in series , not parallel) to see if there is a draw while sitting.<br />Let us know what happens!<br />Good luck
 
Joe Reeves

Joe Reeves

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Re: 1978 70 Johnson runs great but battery goes dead

Randy.... There may be other causes but if you (or someone else) has ever momentarily hooked up the battery backwards, or connected a battery charger to the battery backwards, in all probability the rectifier is shorted out.<br /><br />The rectifier is atached to the engine's starboard side near the engine's wiring terminal block. A metal 1" high flat dome shaped object with a triangular looking base. It has three (3) wires.... 1 Red, 1 Yellow, and 1 Yellow/Gray. Some have two yellows rather than one being yellow/gray.<br /><br />It can be tested as follows:<br /><br />(Small Rectifier Test)<br />(J. Reeves)<br /><br />Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction. <br /><br />Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other. <br /><br />Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires. <br /><br />Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.<br /><br />Before testing the rectifier, disconnect the red positive terminal from the battery, then connect a volt meter between that red positive lead and the positive battery terminal. If you have a short anywhere in the system, it will register on that meter.<br /><br />Leave that positive cable disconnected from the battery while testing the rectifier to avoid any expensive mistakes.
 
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randycisme

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Re: 1978 70 Johnson runs great but battery goes dead

Originally posted by Joe Reeves:<br /> Randy.... There may be other causes but if you (or someone else) has ever momentarily hooked up the battery backwards, or connected a battery charger to the battery backwards, in all probability the rectifier is shorted out.<br /><br />The rectifier is atached to the engine's starboard side near the engine's wiring terminal block. A metal 1" high flat dome shaped object with a triangular looking base. It has three (3) wires.... 1 Red, 1 Yellow, and 1 Yellow/Gray. Some have two yellows rather than one being yellow/gray.<br /><br />It can be tested as follows:<br /><br />(Small Rectifier Test)<br />(J. Reeves)<br /><br />Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction. <br /><br />Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other. <br /><br />Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires. <br /><br />Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.<br /><br />Before testing the rectifier, disconnect the red positive terminal from the battery, then connect a volt meter between that red positive lead and the positive battery terminal. If you have a short anywhere in the system, it will register on that meter.<br /><br />Leave that positive cable disconnected from the battery while testing the rectifier to avoid any expensive mistakes.
Click to expand...
 
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randycisme

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May 3, 2005
Messages
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Re: 1978 70 Johnson runs great but battery goes dead

Thanks for the quick reply Joe. I will check the rectifier as you have described, I haven't had this motor for long, I ran it this last weekend and all was great except for when I tried to run it later that day the battery was dead.
 
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randycisme

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May 3, 2005
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Re: 1978 70 Johnson runs great but battery goes dead

myoutboards,<br />I removed the OEM rectifier from my 70 hp Johnson, the radio shack rectifier that you suggested looks somewhat different, would you mind explaining how to use this one in my application. The rectifier on the motor has a triangle base and 3 wires two yellow and one red, the wires are potted inside of the housing. I was told by the local OMC dealer this unit is used on many motors, the one from radio shack looks like a flat wafer.
 
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phatmanmike

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Oct 24, 2003
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3,869
Re: 1978 70 Johnson runs great but battery goes dead

the new one has 4 terminals.<br /><br />2 terminals for the yellow wires from stator ( AC voltage) <br /><br />1 terminal for your red wire( pos 12V)<br /><br />1 terminal will be your new ground wire, make up a small 6 inch wire to ground the rectifier to the block someplace. the OEM rectifier was grounded were it connected. thats why the OEM has 3 wires and the new has 4
 
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randycisme

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May 3, 2005
Messages
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Re: 1978 70 Johnson runs great but battery goes dead

Just one more question, are the new rectifier terminals specific, are they labeled or do I just pick one and tie it in?
 
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Goldfish

Seaman
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Mar 21, 2005
Messages
50
Re: 1978 70 Johnson runs great but battery goes dead

yes they are specific, you will see 2 that are marked with a ~ that is where the 2 yellow wires go (AC) (Doesnt matter which goes where) one will be marked +, that goes to the red wire (positive) and the other one will be marked - (negative) that goes to engine ground.
 
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