A new issue with my 1984 johnson 75.

JoshKeller84

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Jul 2, 2010
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Took the boat out Sunday, and it ran great. However, I noticed My tach wasnt working, nor was my battery voltage coming up any. I ordered a new rectifier from iboats. Installed the new rectifier tonight, and plugged my tach back into the control box. I noticed I had no power to the gauge (lights, or needle zeroing out) when I turned the key to accessory. Turning the motor over, the light dimly lit, and the gauge zero'ed out, but thats all. Hooked the tach directly to the battery, and the signal wire directly to the grey terminal on the engine, and it worked perfectly. I hooked up the old, non functioning rectifier back up, and plugged the tach back into the control box, and it lit up and zero'd out on the accessory key. Still no tach signal though.

Is this likely a new rectifier issue, or an electrical issue in my control box that isnt showing itself until a properly functioning rectifier is installed?
 

Bosunsmate

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Ive no idea what you are trying to illustrate here.
Disregard your tach at the moment.
Run the engine, check that the battery voltage increases if not then check your stators output to the rectifier.
If thats ok then its either a wiring corrosion issue or something wrong with your new rectifier (unlikely). But if you do hook the battery terminals up backwards they will blow often straight away. There is a rectifier test on this site if you look it up.
Once you have that sorted then you can look at your tach line. I never use a tach when boating as engine noise says it all
 

JoshKeller84

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Its just plain cable going from battery to engine. If the stator or rectifier were bad, would the tach work properly if i hook the power leads to the battery direct, and the tach signal wire to the grey wire? The tqch itself works, and works with the motor, provided i bypass the control box. However, if i reinstall the old, non working, rectifier, the tach lights up and zeros the needle off the control box plug. Howevwr, because its a bad rectifier, no tach signal is present.
 

Bosunsmate

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The tach just goes off the alternating current signal not the level of voltage
 

Bosunsmate

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Putting power lines direct to a battery might cause it to go kaput. Thats ac power not dc
 

JoshKeller84

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What im saying is that the tach has a + and a - connection. When you hook those up, it zeros and thr light turns on. That doesnt happen on the tach plug (coming out of the control box) with the new rectifier installed. If i hook those up to the battery straight, it works as it should. The confusing past is that if i hook up the old non functioning rectifier, the plug on the control box works fine to power up the tach light.
 

flyingscott

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If the rectifier was bad for a long time before you got it yes the charging part of the stator can be bad. How do you know that the voltage was not coming up while you were running it. You need to do all the tests in post #2
 

JoshKeller84

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I have a digital battery gauge on my fish finder. I figured out the problem. Apparently the previous owner decided to do some electrical work inside the control box and was color blind. The purple and grey wires were snipped and teisted together, however they were flip flopped - grey to purple and purple to grey.
 

JoshKeller84

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Spoke too soon. It worked great for 15 minutes. Then tach got erratic for 15 seconds, then stopped working, andbthe bettery stopped charging. I noticed the negative battery cable was very slightly loose. Would this blow the rectifier, or is there a bigger issue at hand?
 

JoshKeller84

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what are some tests to determine what caused this rectifier to blow after 20 minutes of WOT running? I did notice the negative battery cable was loose, and the battery wasnt fully charged (12.4 volts), but wouldnt a short somewhere cause it to blow immediately? Would a fuse on the red rectifier wire prevent this from happening again? Can the tach be hooked up to one of the yellow wires so it can still be used if another rectifier goes out?
 

flyingscott

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You need to start with the stator and check the charging coils they could be shorted. Do you have the manual it will have the values you need, all you need is a good volt/ohm meter. If you don't have the manual go to cdi electronics website they have step by step instructions.
 

phillnjack2

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Apr 30, 2011
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you can test till the cows come, you've simply got the wrong rectifier, check every wie on the engine for chaffing and bas or dirty connections.
also check the earth wire is very clean. then take off the flywheel and carefully look under there for dirt or corrosion. but first thing I would do is get another rectifier.
only cheap to buy in a lot of hobby electrical shops. take original with you and they might even repair that one silly money.
 

JoshKeller84

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Well i tested the stator and one of the leads is coming back as having resistance. Hooked the tach up directly to the yellow wire and it would still bounce around occasionally. Im assuming this confirms i need a new stator?
 

Bosunsmate

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Well i tested the stator and one of the leads is coming back as having resistance. Hooked the tach up directly to the yellow wire and it would still bounce around occasionally. Im assuming this confirms i need a new stator?

you have a short to ground, either in the lead up wiring or the stator
 
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