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1979 Johnson 140, charging + tach problems

S

Scott Wood

New member
Hi Everyone, I've been reading a lot of other posts about charging and tach problems, and I haven't been able to accurately diagnose my problem.

I bought a 1979 Johnson 140 2 weeks ago (it was attached to a really good boat), it had been sitting for a few years so batteries were dead. I put some new sealed batteries in it and took it out on the water. Motor runs good, everything works well except the tach has not worked since I've had it, the speedo and trim gauges didn't work either so I did consider it a big problem.

But camping on the boat last weekend I ran the first battery flat. I started the boat on the 2nd battery then switched back to the first to charge it and noticed all my lights were still dim and my radio didn't work (obviously not charging). When I got home I did some tests with the engine running and confirmed no charge, I did some tests (as found on this forum) and found the rectifier shorting to ground.

Today I replaced the rectifier, now I have some charge (goes up from 12.3v Engine off to 12.5 Idle and 12.6 at what I would guess is about 3000rpm), still nothing on the tach. The grey wire at the terminal block reads 6.2v with the engine running and the red gives battery voltage. Stator has a resistance of 0.8 ohms between the yellow wires disconnected and no continuity with ground.

So I have these questions:

1. Are the sealed batteries going to cause a problem with the old charging system?

2. What do you think my tach problem is?

3. Will I hurt anything by using the boat again this weekend? I'll run the fridge of a separate deep cycle battery this time and only use one battery at a time?
 
1) yes
2) depending on mfg it may be missing ground or it is bad.
3) you could damage stator if rectifier is shorted to ground as it will overheat it...
 
first of all you are starting testing with a not fully charged battery if the meter is reading right..12.3 is too low....charge the battery with a slow charge until the output is 12.6 or 12.7 after the charger is removed.....then look at your dash lights and see if they are still dim...if they are fix that first....thats the simplest problem you see and fixing that may make every thing work...this will be a bad connection between the battery and the 12 volts behind the dash...if they are bright then we will address the charging problem..even if they are bright i would still compare the 12 volts on the console to battery output..they should be exactly the same..

to address the tach problem....take a reading at the term strip on the red output wire...it should read exact battery output....start the engine and run at 2k rpm...after a couple minutes to restore the battery with the used power to start the engine the reading should be more than the battery output..if it is not then change the meter to read ac volts....if you read some ac then the rectifier is at least putting out something...(the ac coming off the stator is not filtered down to a flat line dc...in fact the tach is driven by these pulses)...if there is no ac then the rectifier is not putting out at all...if there is no ac there then leave your meter on ac and read across the two yellow wires coming out of the stator...there should be voltage there...if you read ac there then move the grey wire feeding the tach to one of the yellow wires coming out of the stator and see if the tach works..

at this point please get back to us..write down all of the readings that i asked for and please have them available...
 
Thanks I'll do those tests straight after work, the battery had just come off a smart charger the meter could be reading low (it's a very basic meter). The new rectifier is not shorted to ground, but I was thinking maybe the old bad rectifier might have blown the old tacho up, I don't have access to another tacho at the moment but I'm less worried about that for now.
 
Fwiw. A bad rectumfrier can ruin your tach, and even blow up your battery.
 

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papyson said:
first of all you are starting testing with a not fully charged battery if the meter is reading right..12.3 is too low....charge the battery with a slow charge until the output is 12.6 or 12.7 after the charger is removed.....then look at your dash lights and see if they are still dim...if they are fix that first....thats the simplest problem you see and fixing that may make every thing work...this will be a bad connection between the battery and the 12 volts behind the dash...if they are bright then we will address the charging problem..even if they are bright i would still compare the 12 volts on the console to battery output..they should be exactly the same..

to address the tach problem....take a reading at the term strip on the red output wire...it should read exact battery output....start the engine and run at 2k rpm...after a couple minutes to restore the battery with the used power to start the engine the reading should be more than the battery output..if it is not then change the meter to read ac volts....if you read some ac then the rectifier is at least putting out something...(the ac coming off the stator is not filtered down to a flat line dc...in fact the tach is driven by these pulses)...if there is no ac then the rectifier is not putting out at all...if there is no ac there then leave your meter on ac and read across the two yellow wires coming out of the stator...there should be voltage there...if you read ac there then move the grey wire feeding the tach to one of the yellow wires coming out of the stator and see if the tach works..

at this point please get back to us..write down all of the readings that i asked for and please have them available...
Click to expand...

Ok, this is what I have:

Engine running at a guessed 2000rpm, has been running for a few mins, I have 12.95v DC at red output wire which is slightly higher that battery voltage. I'm getting a constant 8.2VAC at the either of the yellow stator wires and an erratic AC voltage at the red wire. Moving the tach wire had no effect on it's operation, I haven't seen the needle move yet. Dash lights, radio etc have been working fine since the batteries have been charged. It may also be worth noting the outboard runs fine with the isolator switched to off once running.
 
Last edited:
you can use the boat..its saturday morning and you asked if you could use it this weekend....i would isolate my ignition battery however and place he aux load such as fridge on the 2nd battery..after you have run the boat for 30 minutes or so take another reading on the battery posts with the engine doing 2 or 3 k rpm...that reading should go higher than 12.95 volts..on a rectifier only system i would expect in the 15 volt range...maybe a tad higher..that is with just the motor on the ignition battery...

i dont know what kind of switching arrangement you have on the batteries but the rectifier should never be without a load with the motor running..another note here on a boat charging system....especially the one you have..it is designed to keep a charged battery topped off...it is not designed to furnish a heavy current load such as a fridge...so make sure both your batteries are topped off when you put the boat in the water..

i forgot to tell you to take the load off the charging system except for the motor and bilge pump...what was the load when you took the readings?

i have to make an emergency trip out of state so may be unavailable for a few days..i will have a laptop but dont know how much time i will have...so i need someone to step in on this problem...
 
papyson said:
you can use the boat..its saturday morning and you asked if you could use it this weekend....i would isolate my ignition battery however and place he aux load such as fridge on the 2nd battery..after you have run the boat for 30 minutes or so take another reading on the battery posts with the engine doing 2 or 3 k rpm...that reading should go higher than 12.95 volts..on a rectifier only system i would expect in the 15 volt range...maybe a tad higher..that is with just the motor on the ignition battery...

i dont know what kind of switching arrangement you have on the batteries but the rectifier should never be without a load with the motor running..another note here on a boat charging system....especially the one you have..it is designed to keep a charged battery topped off...it is not designed to furnish a heavy current load such as a fridge...so make sure both your batteries are topped off when you put the boat in the water..

i forgot to tell you to take the load off the charging system except for the motor and bilge pump...what was the load when you took the readings?

i have to make an emergency trip out of state so may be unavailable for a few days..i will have a laptop but dont know how much time i will have...so i need someone to step in on this problem...
Click to expand...

I must apologize, I didn't see this reply until after I had already set off for the weekend, but I went anyway and had no problems. I lost faith in my multimeter, It was sometimes showing 5v on a known good battery, so I didn't get any readings that I trust. I bought a new multimeter yesterday so I'll retest everything when I get a chance. The boat went well anyway, I only used the one battery and was able to use nav lights, anchor light and radio plus normal starting tilt/trim etc with no problem all weekend, bilge pump is auto but never actually ran all weekend, stayed 2 nights on board and did about 6 engine hours with no trouble. I had a separate divorced deep cycle battery to run the fridge plus a spare battery that wasn't required. I guess I'm going to need solar for longer stays to power the fridge.
 
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