1979 70hp johnson charging problem

toneinvic

Cadet
Joined
May 6, 2002
Messages
8
hi, I checked my battery voltage yesterday and it read 12.7V.......the same running or not. I assume my charging system isn't working at all. Can anyone suggest the most likley problem??
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: 1979 70hp johnson charging problem

Do you have a tachometer? Did it quit? If so, it's the rectifier. That's the usual culprit. All the smoke probably leaked out of it.<br /><br />c/6<br />Hooty
 

toneinvic

Cadet
Joined
May 6, 2002
Messages
8
Re: 1979 70hp johnson charging problem

I checked the rectifier and it was faulty. I replaced it and now the charging voltage at idle is 16.8V !!! Is that normal?
 

Lonestar69

Recruit
Joined
Jul 3, 2005
Messages
3
Re: 1979 70hp johnson charging problem

I know that this thread is a bit old, but it describes the exact problem I am having with my 1975 Johnson 70...12.6 volts running or not.<br /><br />I do not have a tach and I read another post about how to check the rectifier which I am going to do as soon as it stops raining.<br /><br />I have two questions: <br /><br />1. If the rectifier should check out ok what else could be the problem?<br /><br />2. I have heard that using a deep cycle battery can cause problems, is this true? If so, why?<br /><br />Thanks, Todd
 

DHPMARINE

Captain
Joined
Dec 16, 2003
Messages
3,688
Re: 1979 70hp johnson charging problem

I hate to speculate.So do the rectifier test and let us know.Deep Cycle battery wil not cause any problem the regular battery can't.<br /><br />DHP
 

Lonestar69

Recruit
Joined
Jul 3, 2005
Messages
3
Re: 1979 70hp johnson charging problem

I tested the rectifier and it shows bad.<br /><br />I have a 25 amp 50 volt full wave bridge rectifier that I had picked up from Radio Shack...would that work?<br /><br />Thanks, Todd
 

DHPMARINE

Captain
Joined
Dec 16, 2003
Messages
3,688
Re: 1979 70hp johnson charging problem

Probably might work,but new part is $50.00,and correct,and will work.If you burn out the wiring harness,it is NLA,and Radio Shack doesn't have them either.<br /><br />Your choice (grin)<br /><br />DHP
 

Lonestar69

Recruit
Joined
Jul 3, 2005
Messages
3
Re: 1979 70hp johnson charging problem

I agree, just a thought. Funny thing is I have seen a price spread from around $25 to $140.<br /><br />The local marine parts shop here has one on the shelf for $49 ... why such a spread?<br /><br />Thanks for the help.<br /><br />Todd
 
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