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1998 Johnson 90-HP Electrical Problem
|Author||Topic: 1998 Johnson 90-HP Electrical Problem|
posted 08-25-2008 11:03 AM ET (US)
Good morning all. My 1998 Johnson 90 cranks and runs fine but the tachometer sometimes works at startup. But after a minute or so drops to zero. Other times doesn't work at all.
The on-dash voltmeter reads just over 12 at all RPM. Engine doesn't appear to be charging, although I haven't had a dead battery yet.
The System Check gauge does not work. This is the separate two-inch gauge in dash. It used to work according to the previous owner, but now does nothing at startup. Any ideas how to check?
Local shadetree mechanic said [the source of all these problems was a failure of the] voltage regulator. Any way to test [the voltage regulaor]? I would rather test before dropping $300. Any good place to buy [the voltage regulator] online?
posted 08-25-2008 11:17 AM ET (US)
You can generally deduce the state of the engine's battery charging circuit by measuring the battery voltage with an accurate voltmeter while the engine is running. If the engine battery charging circuit is working properly, the battery voltage should be dragged up to at least 13.2 volts.
The panel mounted voltmeters provided as accessories in most boats are not sufficiently accurate to make much of a diagnosis. Connect an accurate meter and measure the voltage. If it is below 13.2-volts, we can offer some other advice for more diagnostic tests.
If you want to perform service on your motor, I recommend you get the OEM service manual. In the case of a 1998 Johnson, I believe they are still available from the original publisher.
posted 08-25-2008 11:21 AM ET (US)
Are the tachometer, System Check, and charging functions all from the rectifier-regulator? If there is any way to check this regulator for output?
Going to pick up a manual today.
posted 08-25-2008 11:26 AM ET (US)
The output of the regulator is connected directly to the battery. When you measure the battery voltage, you will be measuring the regulator output.
Also, in any battery-operated system which has electrical problems, the first component to test and eliminate as a source of the problem is the battery itself. A battery with a shorted cell will not be able to have its terminal voltage rise above 11-volts. I recommend you first test the battery to be certain it is operating properly.
posted 08-25-2008 11:38 AM ET (US)
Yesterday the battery was replaced with a new [battery] that was fully charged before installation. Still no System Check lights, no tachometer, no startup buzzer.
Reading after engine start at battery terminals was 12.4V. Drops to near 11 when trim is engaged, then back to 12.3 to 12.4.
posted 08-26-2008 01:01 AM ET (US)
The System Check guage contains all the electronics to make the self-test lights work and to sound the warning horn.It has nothing to do with your charging system. If your indicator lights are in the tach, then you have a bad guage or possibly a lack of power reaching the gauge.
Remove and reinstall the 8-pin connector on the back of the gauge. Also make sure there is 12V+ on the violet (purple) wire with the keyswitch ON, and that the black wire is at ground. Substituting a known good gauge is the quickest way to troubleshoot one.
posted 08-26-2008 08:03 AM ET (US)
thanks for the replies jimh and seahorse.
One other question...isn't the purple wire the one that originates from the voltage regulator/rectifier and provides power for the systemcheck and also provides a signal for the tach? Looks as though purple also ties into the VRO.
If the voltage regulator/rectifier was bad wouldn't that cause all three symptoms...non-functioning tach, no system check and no batt charging? At least this is the way it appears in the service book.
I will not be able to get back to it until this weekend, however I will check what was described above then.
posted 08-26-2008 08:17 AM ET (US)
<<<<<<One other question...isn't the purple wire the one that originates from the voltage regulator/rectifier and provides power for the systemcheck and also provides a signal for the tach? Looks as though purple also ties into the VRO.>>>>>>
The violet (purple) wire delivers 12V trhough the key switch ON position to power the gauges, power the "VRO" alarm circuitry, and provides the reference voltage at the regulator. Newer regulators do not use the voltage sense wire.
posted 08-26-2008 09:29 AM ET (US)
For information on the wiring associated with the ignition key switch see
If your motor battery charging circuit only pulls the battery voltage to 12.4 volts you have no battery charging at all. A battery with a terminal voltage of 12.4-volts is in a state of 35-percent discharged.
The battery charging circuit should pull the battery terminal voltage up to at least 13.2-volts and possibly as high as 14-volts during maximum charging current. If your voltage reading is accurate, it implies a failure of your motor's battery charging circuit.
posted 08-26-2008 10:18 AM ET (US)
So, I should be able to find +12V between A on the key switch and M with the key in the "on" position regardless of the regulator. Then I will need to check the violet wire to each gauge to make certain I am getting +12V, correct?
I'll test the charging system separate per the book instructions to see what is going on with battery charging.
Sounds like there may be two seperate problems. Thanks for all your help!!
posted 08-26-2008 10:21 AM ET (US)
One more thing...how easy it is to take apart the throttle to get to the key switch? This is the combo type throttle and keyswitch type...with little "fins" above the key switch.
Is the buzzer integral on this type, or located under the dash?
posted 08-26-2008 12:11 PM ET (US)
It may be that you have misinterpreted the legends of the terminals as shown in the pictorial diagram. The M terminal is next to the B terminal. Please re-read the article, review the illustrations, and the text that accompanies them.
posted 08-26-2008 03:25 PM ET (US)
Yep, thinking backwards.
posted 08-26-2008 05:52 PM ET (US)
If you repair the wiring so that 12V is present at the violet (purple) wire, you may be pleasantly surprised to see your charging system operational again as long as the rest of the parts are OK.
posted 08-26-2008 09:53 PM ET (US)
The System Check gauge is not directly affected by the battery charging circuit. If this gauge is not functioning there is likely a problem with the voltage being supplied to it.
The System Check gauge functions in this manner:
--when the ignition key is moved to ON from OFF;
The aural alarm is a separate module; it is not part of the System Check gauge. The aural alarm sounder is often located in the base of the remote throttle and shift controls if they have an integral ignition key. The aural alarm is triggered by the System Check gauge output circuit.
posted 08-28-2008 04:29 PM ET (US)
Thanks for your help. I am going back to it this weekend and testing it all.
The guy that owned it before said the systemcheck used to work, and that the tach was not working before systemcheck went out.
After reading and studying the diagrams, etc I am thinking it is probably more than one issue.
Will let you know what I find.
posted 08-28-2008 06:08 PM ET (US)
A bad ground (or battery negative terminal) lead can affect many circuits. Check that the battery negative circuit to the dash panel area is good.
posted 08-30-2008 07:41 AM ET (US)
Regulator/rectifier was problem #1. Output voltage and tach are now back functioning.
Side note...if you use the Seloc manual it tells you the torque for the bolts on the rectifier are 60-86 in lbs or 80 to 120 in lbs. DO NOT go above 80...these bolts are alum and they will snap...learned that the hard way yesterday.
Systemcheck is still out...I have proper voltage between purple and black pins in the 8 wire harness...only thing I can figure is a bad gauge.
I am starting to think someone may have hooked the battery up backwards or lightning hit this boat at some time in the past...volt reg, cd player, depth finder and systemcheck were all out (non-functioning)
posted 08-30-2008 09:17 AM ET (US)
Your diagnostic suspicion that there was a prior polarity reversal in connecting the primary battery is likely correct. It seems to be a common one-time mistake, particularly when the primary battery cables are not well identified or the battery terminals are obscurely marked.
A polarity reversal generally does take out the rectifier. I don't know what it does to the System Check gauge.
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